Jump to content

Daggernose shark: Difference between revisions

From Wikipedia, the free encyclopedia
Browse history interactively
← Previous edit
Content deleted Content added
VisualWikitext
ZéroBot (talk | contribs)
704,777 edits
m r2.7.1) (Robot: Adding ja:ツバクロザメ
m Disambiguating links to Catshark (link changed to Scyliorhinidae) using DisamAssist.
 
(53 intermediate revisions by 38 users not shown)
Line 1: Line 1:

{{Taxobox
{{Short description|Species of shark}}{{Distinguish|text=the [[Goblin shark]] which has a similar snout}}{{Speciesbox
| name = Daggernose shark
| name = Daggernose shark
| image = Isogomphodon oxyrhynchus drawing.jpg
| image = Isogomphodon oxyrhynchus (Müller & Henle, 1839) 2432753577.jpg
| image_width = 240px
| status = CR
| status = CR
| status_system = IUCN3.1
| status_system = IUCN3.1
| status_ref = <ref name="iucn">{{IUCN2008 |assessors=Lessa, R., P. Charvet-Almeida, F.M. Santana and Z. Almeida |year=2006 |id=60218 |title=Isogomphodon oxyrhynchus |downloaded=September 2, 2009}}</ref>
| status_ref = <ref name="iucn status 19 November 2021">{{cite iucn |author=Pollom, R. |author2=Charvet, P. |author3=Faria, V. |author4=Herman, K. |author5=Lasso-Alcalá, O. |author6=Marcante, F. |author7=Nunes, J. |author8=Rincon, G. |author9=Kyne, P.M. |date=2020 |title=''Isogomphodon oxyrhynchus'' |volume=2020 |page=e.T60218A3094144 |doi=10.2305/IUCN.UK.2020-3.RLTS.T60218A3094144.en |access-date=19 November 2021}}</ref>
| regnum = [[Animal]]ia
| genus = Isogomphodon
⚫
| parent_authority = [[Theodore Gill|T. N. Gill]], 1862
| phylum = [[Chordate|Chordata]]
⚫
| species = oxyrhynchus
| classis = [[Chondrichthyes]]
⚫
| authority = ([[Johannes Peter Müller|J. P. Müller]] & [[Friedrich Gustav Jakob Henle|Henle]], 1839)
| subclassis = [[Elasmobranchii]]
| ordo = [[Carcharhiniformes]]
| familia = [[Carcharhinidae]]
| genus = '''''Isogomphodon'''''
⚫
| genus_authority = [[Theodore Gill|T. N. Gill]], 1862
⚫
| species = '''''I. oxyrhynchus'''''
| binomial = ''Isogomphodon oxyrhynchus''
⚫
| binomial_authority = ([[Johannes Peter Müller|J. P. Müller]] &amp; [[Friedrich Gustav Jakob Henle|Henle]], 1839)
| range_map = Isogomphodon oxyrhynchus distmap.png
| range_map = Isogomphodon oxyrhynchus distmap.png
| range_map_width = 240px
| range_map_caption = Range of the daggernose shark
| range_map_caption = Range of the daggernose shark
| synonyms = ''Carcharias oxyrhynchus'' <small>Müller & Henle, 1839</small>
| synonyms = ''Carcharias oxyrhynchus'' <small>Müller & Henle, 1839</small>
}}
}}


The '''daggernose shark''' (''Isogomphodon oxyrhynchus'') is a little-known [[species]] of [[requiem shark]], [[family (biology)|family]] [[Carcharhinidae]], and the only extant member of its [[genus]]. It occurs in shallow [[tropical]] waters off northeastern [[South America]] from [[Trinidad]] to northern [[Brazil]], favoring muddy habitats such as [[mangrove]]s, [[estuaries]], and river mouths, though it is intolerant of [[fresh water]]. A relatively small shark typically reaching {{convert|1.5|m|ft|abbr=on}} in length, the daggernose shark is unmistakable for its elongated, flattened, and pointed snout, tiny eyes, and large paddle-shaped [[pectoral fin]]s.
The '''daggernose shark''' ('''''Isogomphodon oxyrhynchus''''') is a little-known [[species]] of [[requiem shark]], in the [[family (biology)|family]] [[Requiem shark|Carcharhinidae]], and the only extant member of its [[genus]]. It inhabits shallow [[tropical]] waters off northeastern [[South America]], from [[Trinidad]] to northern [[Brazil]], favoring muddy habitats such as [[mangrove]]s, [[estuaries]], and river mouths, though it is intolerant of [[fresh water]]. A relatively small shark typically reaching {{convert|1.5|m|ft|abbr=on}} in length, the daggernose shark is unmistakable for its elongated, flattened, and pointed snout, tiny eyes, and large paddle-shaped [[pectoral fin]]s.


Daggernose sharks are [[predator]]s of small [[schooling fish]]es. Reproduction is [[viviparous]], with females give birth to 2–8 pups every other year during the [[rainy season]]; this species is capable of shifting the timing of its reproductive cycle by several months in response to the environment. Harmless to humans, the daggernose shark is caught for food and as [[bycatch]] in [[artisan fishing|artisanal]] and [[commercial fishing|commercial fisheries]]. Limited in range and slow-reproducing, it has been assessed as [[Critically Endangered]] by [[International Union for Conservation of Nature]] in light of a steep population decline in recent years.
Daggernose sharks are [[predator]]s of small [[schooling fish]]es. Its reproduction is [[viviparous]], with females give birth to 2–8 pups every other year during the [[rainy season]]; this species is capable of shifting the timing of its reproductive cycle by several months in response to the environment. Harmless to humans, the daggernose shark is caught for food and as [[bycatch]] in [[artisan fishing|artisanal]] and [[commercial fishing|commercial fisheries]]. Limited in range and slow-reproducing, it has been assessed as [[Critically Endangered]] by [[International Union for Conservation of Nature]] in light of a steep population decline in recent years. The current population is believed to be extremely low, with no more than 250 individuals believed to be in existence as of 2023.<ref>Lessa, Rosangela, et al. “Close to Extinction? The Collapse of the Endemic Daggernose Shark (Isogomphodon Oxyrhynchus) off Brazil.” Global Ecology and Conservation, vol. 7, 2016, pp. 70–81., doi:10.1016/j.gecco.2016.04.003.</ref> Indeed, it may even be in reproductive collapse, in which case it will likely become extinct in the near future.<ref name="blogs.scientificamerican.com">{{Cite web|url=http://blogs.scientificamerican.com/extinction-countdown/the-daggernose-shark-is-near-extinction/?wt.mc=SA_Facebook-Share|title = The Daggernose Shark is Near Extinction}}</ref>


==Taxonomy and phylogeny==
==Taxonomy and phylogeny==
[[Image:Carcharias oxyrhynchus by muller and henle.png|thumb|left|The illustration that accompanied Müller and Henle's original description.]]
[[File:Carcharias oxyrhynchus by muller and henle.png|thumb|left|The illustration that accompanied Müller and Henle's original description.]]
The first scientific description of the daggernose shark, as ''Carcharias oxyrhynchus'', was published by German biologists [[Johannes Peter Müller]] and [[Friedrich Gustav Jakob Henle]] in their 1839 ''Systematische Beschreibung der Plagiostomen''. They chose the [[specific name (zoology)|specific epithet]] ''oxyrhynchus'', from the Greek ''oxys'' ("sharp" or "pointed") and ''rhynchos'' ("nose"). In 1862, American [[ichthyologist]] [[Theodore Gill]] coined the genus ''Isogomphodon'' for this species, from the Greek ''isos'' ("equal"), ''gomphos'' ("nail" or "peg"), and ''odous'' ("tooth"). However, ''Isogomphodon'' was subsequently relegated to being a [[synonym (taxonomy)|synonym]] of ''[[Carcharhinus]]'', until it was resurrected by shark authority [[Stewart Springer]] in 1950.<ref name="compagno">{{cite book |author=Compagno, L.J.V. |date=1984 |title=Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date |place=Rome |publisher=Food and Agricultural Organization |isbn=9251013845 |pages=510–511}}</ref> Regardless of its taxonomic validity, ''Isogomphodon'', along with the genera ''[[Nasolamia]]'' and ''[[Prionace]]'', is closely related to ''Carcharhinus''. An [[extinct]] relative, ''I. acuarius'', dates back to the [[Middle Eocene]] (45 [[mya (unit)|Ma]]).<ref>{{cite book |title=Biology of Sharks and Their Relatives |author=Carrier, J.C., J.A. Musick and M.R. Heithaus |publisher=CRC Press |date=2004 |isbn=084931514X |pages=51–52}}</ref>
The first scientific description of the daggernose shark, as ''Carcharias oxyrhynchus'', was published by German biologists [[Johannes Peter Müller]] and [[Friedrich Gustav Jakob Henle]] in their 1839 ''Systematische Beschreibung der Plagiostomen''. They chose the [[specific name (zoology)|specific epithet]] ''oxyrhynchus'', from the Greek ''{{lang|grc-Latn|oxys}}'' ("sharp" or "pointed") and ''{{lang|grc-Latn|rhynchos}}'' ("nose"). In 1862, American [[ichthyologist]] [[Theodore Gill]] coined the genius ''Isogomphodon'' for this species, from the Greek ''{{lang|grc-Latn|isos}}'' ("equal"), ''{{lang|grc-Latn|gomphos}}'' ("nail" or "peg"), and ''{{lang|grc-Latn|odous}}'' ("tooth"). However, ''Isogomphodon'' was subsequently relegated to being a [[synonym (taxonomy)|synonym]] of ''[[Carcharhinus]]'', until it was resurrected by shark authority [[Stewart Springer]] in 1950.<ref name="compagno">{{cite book |author=Compagno, L.J.V. |date=1984 |title=Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date |place=Rome |publisher=Food and Agricultural Organization |isbn=92-5-101384-5 |pages=510–511}}</ref> Regardless of its taxonomic validity, ''Isogomphodon'', along with the genera ''[[Nasolamia]]'' and ''[[Prionace]]'', is closely related to ''Carcharhinus''. An [[extinct]] relative, ''I. acuarius'', dates back to the [[Middle Eocene]] (45 [[mya (unit)|Ma]]).<ref>{{cite book |title=Biology of Sharks and Their Relatives |author=Carrier, J.C. |author2=J.A. Musick |author3=M.R. Heithaus |name-list-style=amp |publisher=CRC Press |date=2004 |isbn=0-8493-1514-X |pages=51–52}}</ref>


==Distribution and habitat==
==Distribution and habitat==
The daggernose shark is found along the northeastern coast of [[South America]], off [[Trinidad]], [[Guyana]], [[Suriname]], [[French Guyana]], and northern [[Brazil]].<ref name="compagno"/> It reportedly occurs as far south as [[Valença, Bahia|Valença]] in the central Brazilian state of [[Bahia]], though [[fishery]] surveys have not detected this species in the area and it is apparently unknown to local fishermen.<ref name="iucn"/>
The daggernose shark is found along the northeastern coast of [[South America]], off [[Trinidad]], [[Guyana]], [[Suriname]], [[French Guiana]], and northern [[Brazil]].<ref name="compagno"/> It reportedly occurs as far south as [[Valença, Bahia|Valença]] in the central Brazilian state of [[Bahia]], though [[fishery]] surveys have not detected this species in the area and it is apparently unknown to local fishermen.<ref name="iucn status 19 November 2021" />


An inhabitant of coastal waters at a depth of {{convert|4|-|40|m|ft|abbr=on}}, the daggernose shark prefers highly turbid waters and decreases in number with increasing water clarity. Females tend to be found at greater depths than males.<ref name="fowler et al">{{cite book |author=Fowler, S.L., R.D. Cavanagh, M. Camhi, G.H. Burgess, G.M. Cailliet, S.V. Fordham, C.A. Simpfendorfer, and J.A. Musick |title=Sharks, Rays and Chimaeras: The Status of the Chondrichthyan Fishes |publisher=International Union for Conservation of Nature and Natural Resources |date=2005 |isbn=2831707005 |pages=306–308}}</ref> Its range encompasses a wide [[continental shelf]] with a humid [[tropical]] [[climate]], extensive [[mangrove]]s, and draining by numerous rivers including the [[Amazon River|Amazon]]. Water [[salinity]] in this area ranges from 20 to 34 ppt, while the [[tide|tidal amplitude]] can measure up to {{convert|7|m|ft|abbr=on}}.<ref name="iucn"/> Daggernose sharks are most common over shallow muddy banks and in [[estuary|estuaries]] and river mouths. It seems to be intolerant of low salinity, moving inshore during the [[dry season]] (June to November) and offshore during the [[rainy season]] (December to May).<ref name="compagno et al">{{cite book |author=Compagno, L.J.V., M. Dando and S. Fowler |title=Sharks of the World |publisher=Princeton University Press |date=2005 |isbn=9780691120720 |page=313}}</ref> This species is not known to make long-distance movements, though some local seasonal movements are possible.<ref name="iucn"/>
An inhabitant of coastal waters at a depth of {{convert|4|-|40|m|ft|abbr=on}}, the daggernose shark prefers highly turbid waters and decreases in number with increasing water clarity. Females tend to be found at greater depths than males.<ref name="fowler et al">{{cite book |author=Fowler, S.L. |author2=R.D. Cavanagh |author3=M. Camhi |author4=G.H. Burgess |author5=G.M. Cailliet |author6=S.V. Fordham|author7=C.A. Simpfendorfer |author8=J.A. Musick |name-list-style=amp |title=Sharks, Rays and Chimaeras: The Status of the Chondrichthyan Fishes |publisher=International Union for Conservation of Nature and Natural Resources |date=2005 |isbn=2-8317-0700-5 |pages=306–308}}</ref> Its range encompasses a wide [[continental shelf]] with a humid [[tropical]] [[climate]], extensive [[mangrove]]s, and draining by numerous rivers including the [[Amazon River|Amazon]]. Water [[salinity]] in this area ranges from 20 to 34 ppt, while the [[tide|tidal amplitude]] can measure up to {{convert|7|m|ft|abbr=on}}.<ref name="iucn status 19 November 2021" /> Daggernose sharks are most common over shallow muddy banks and in [[estuary|estuaries]] and river mouths. It seems to be intolerant of low salinity, moving inshore during the [[dry season]] (June to November) and offshore during the [[rainy season]] (December to May).<ref name="compagno et al">{{cite book |author=Compagno, L.J.V. |author2=M. Dando |author3=S. Fowler |name-list-style=amp |title=Sharks of the World |publisher=Princeton University Press |date=2005 |isbn=978-0-691-12072-0 |page=313}}</ref> This species is not known to make long-distance movements, though some local seasonal movements are possible.<ref name="iucn status 19 November 2021" />


==Description==
==Description==
Line 40: Line 32:
As its [[common name]] suggests, the daggernose shark has a very long, flattened snout with a pointed tip and an acutely triangular profile from above. The eyes are circular and minute in size, with [[nictitating membrane]]s (a protective third [[eyelid]]). The [[nostril]]s are small, without prominent nasal skin flaps. There are short but deep furrows at the corners of the mouth on both jaws. The tooth rows number 49–60 and 49–56 in the upper and lower jaws respectively. Each tooth has a single narrow, upright cusp; the upper teeth are slightly broader and flatter than the lower teeth, with serrated rather than smooth edges.<ref name="compagno"/>
As its [[common name]] suggests, the daggernose shark has a very long, flattened snout with a pointed tip and an acutely triangular profile from above. The eyes are circular and minute in size, with [[nictitating membrane]]s (a protective third [[eyelid]]). The [[nostril]]s are small, without prominent nasal skin flaps. There are short but deep furrows at the corners of the mouth on both jaws. The tooth rows number 49–60 and 49–56 in the upper and lower jaws respectively. Each tooth has a single narrow, upright cusp; the upper teeth are slightly broader and flatter than the lower teeth, with serrated rather than smooth edges.<ref name="compagno"/>


The body is robustly built, with large, broad, paddle-like [[pectoral fin]]s that originate under the fifth [[gill slit]]. The first [[dorsal fin]] originates over the posterior half of the pectoral fin bases. The second dorsal fin is about half as tall as the first and located over or slightly ahead of the [[anal fin]]. The anal fin is smaller than the second dorsal fin and has a deep notch in the rear margin. The [[caudal fin]] has a well-developed lower lobe and is preceded by a crescent-shaped notch on the upper side of the [[caudal peduncle]]. The coloration is a plain gray above, sometimes with a brownish or yellowish cast, and lighter below.<ref name="compagno"/> Males attain a length of {{convert|1.4|m|ft|abbr=on}} and females {{convert|1.6|m|ft|abbr=on}}.<ref name="iucn"/> There are unsubstantiated records of individuals {{convert|2.0|-|2.4|m|ft|abbr=on}} long.<ref name="compagno"/> The maximum known weight is {{convert|13|kg|lb|abbr=on}}.<ref name="fowler et al"/>
The body is robustly built, with large, broad, paddle-like [[pectoral fin]]s that originate under the fifth [[gill slit]]. The first [[dorsal fin]] originates over the posterior half of the pectoral fin bases. The second dorsal fin is about half as tall as the first and located over or slightly ahead of the [[anal fin]]. The anal fin is smaller than the second dorsal fin and has a deep notch in the rear margin. The [[caudal fin]] has a well-developed lower lobe and is preceded by a crescent-shaped notch on the upper side of the [[caudal peduncle]]. The coloration is a plain gray above, sometimes with a brownish or yellowish cast, and lighter below.<ref name="compagno"/> Males attain a length of {{convert|1.4|m|ft|abbr=on}} and females {{convert|1.6|m|ft|abbr=on}}.<ref name="iucn status 19 November 2021" /> There are unsubstantiated records of individuals {{convert|2.0|-|2.4|m|ft|abbr=on}} long.<ref name="compagno"/> The maximum known weight is {{convert|13|kg|lb|abbr=on}}.<ref name="fowler et al"/>


==Biology and ecology==
==Biology and ecology==
The dominant shark species within the daggernose shark's range are the [[smalltail shark]] (''Carcharhinus porosus'') and the [[bonnethead]] (''Sphyrna tiburo'').<ref name="iucn"/> Its elongated snout and tiny eyes are likely consequences of living in murky sediment-laden waters, reflecting an [[adaptation|adaptive]] emphasis on [[electroreception]] and other [[rostrum (anatomy)|rostral]] senses rather than vision. The snout bears a superficial similarity to the [[goblin shark]] (''Mitsukurina owstoni''), some ''[[Apristurus]]'' [[catshark]]s, and the [[Rhinochimaeridae|long-nosed chimaeras]], all found in the [[deep sea]].<ref name="fowler et al"/> With long jaws and numerous small teeth, the daggernose shark is well-suited for capturing the small [[schooling fish]]es that comprise most of its diet. Known prey taken include [[herring]], [[anchovy|anchovies]], [[catfish]], and [[Sciaenidae|croakers]].<ref name="compagno"/>
The dominant shark species within the daggernose shark's range are the [[smalltail shark]] (''Carcharhinus porosus'') and the [[bonnethead]] (''Sphyrna tiburo'').<ref name="iucn status 19 November 2021" /> Its elongated snout and tiny eyes are likely consequences of living in murky sediment-laden waters, reflecting an [[adaptation|adaptive]] emphasis on [[electroreception]] and other [[rostrum (anatomy)|rostral]] senses rather than vision. The snout bears a superficial similarity to the [[goblin shark]] (''Mitsukurina owstoni''), some ''[[Apristurus]]'' [[Scyliorhinidae|catshark]]s, and the [[Rhinochimaeridae|long-nosed chimaeras]], all found in the [[deep sea]].<ref name="fowler et al"/> With long jaws and numerous small teeth, the daggernose shark is well-suited for capturing the small [[schooling fish]]es that comprise most of its diet. Known prey taken include [[herring]], [[anchovy|anchovies]], [[catfish]], and [[Sciaenidae|croakers]].<ref name="compagno"/>


The daggernose shark is [[viviparous]]; once the developing [[embryo]]s exhaust their supply of [[yolk]], the depleted [[yolk sac]] is converted into a [[placenta]]l connection through which the mother delivers sustenance. Females give birth to litters of 2–8 pups every other year, following a year-long [[gestation period]]. There is no correlation between female size and number of offspring.<ref name="fowler et al"/> [[Mating]] and parturition take place over a roughly six-month period from the beginning to the end of the rainy season. However, the daggernose shark is capable of shifting the timing of its reproductive cycle by at least four months, possibly in response to varying environmental conditions.<ref>{{cite journal |author=Lessa, R., F.M.Santana and P. Duarte-Neto |title=A critical appraisal of marginal increment analysis for assessing temporal periodicity in band formation among tropical sharks |journal=Environmental Biology of Fishes |volume=77 |issue=3–4 |pages=309–215 |date=December 2006 |doi=10.1007/s10641-006-9111-7}}</ref> Females move into shallow coastal nurseries to give birth; one important nursery exists off Brazilian state of [[Maranhão]].<ref name="fowler et al"/>
The daggernose shark is [[viviparous]]; once the developing [[embryo]]s exhaust their supply of [[yolk]], the depleted [[yolk sac]] is converted into a [[placenta]]l connection through which the mother delivers sustenance. Females give birth to litters of 2–8 pups every other year, following a year-long [[gestation period]]. There is no correlation between female size and number of offspring.<ref name="fowler et al"/> [[Mating]] and parturition take place over a roughly six-month period from the beginning to the end of the rainy season. However, the daggernose shark is capable of shifting the timing of its reproductive cycle by at least four months, possibly in response to varying environmental conditions.<ref>{{cite journal |author=Lessa, R. |author2=F.M.Santana |author3=P. Duarte-Neto |name-list-style=amp |title=A critical appraisal of marginal increment analysis for assessing temporal periodicity in band formation among tropical sharks |journal=Environmental Biology of Fishes |volume=77 |issue=3–4 |pages=309–315|date=December 2006 |doi=10.1007/s10641-006-9111-7|bibcode=2006EnvBF..77..309L |s2cid=23735874 }}</ref> Females move into shallow coastal nurseries to give birth; one important nursery exists off Brazilian state of [[Maranhão]].<ref name="fowler et al"/>


Newly born daggernose sharks measure {{convert|38|-|43|cm|in|abbr=on}} in length.<ref name="fowler et al"/> Males [[sexual maturation|mature]] at {{convert|103|cm|in|abbr=on}} long, corresponding to an age of 5–6 years, while females mature at {{convert|115|cm|in|abbr=on}} long, corresponding to an age of 6–7 years. The [[longevity|lifespan]] of males has been measured at up to 7 years, and females 12 years; extrapolating from growth rates suggest that the largest known males and females may be 12 and 20 years old respectively.<ref>{{cite journal |author=Lessa, R., F.M. Santana, V. Batista and Z. Almeida |title=Age and growth of the daggernose shark, ''Isogomphodon oxyrhynchus'', from northern Brazil |journal=Marine and Freshwater Research |volume=51 |issue=4 |pages=339–347|date=2000 |doi=10.1071/MF99125}}</ref>
Newly born daggernose sharks measure {{convert|38|-|43|cm|in|abbr=on}} in length.<ref name="fowler et al"/> Males [[sexual maturation|mature]] at {{convert|103|cm|in|abbr=on}} long, corresponding to an age of 5–6 years, while females mature at {{convert|115|cm|in|abbr=on}} long, corresponding to an age of 6–7 years. The [[longevity|lifespan]] of males has been measured at up to 7 years, and females 12 years; extrapolating from growth rates suggest that the largest known males and females may be 12 and 20 years old respectively.<ref>{{cite journal |author=Lessa, R. |author2=F.M. Santana |author3=V. Batista |author4=Z. Almeida |name-list-style=amp |title=Age and growth of the daggernose shark, ''Isogomphodon oxyrhynchus'', from northern Brazil |journal=Marine and Freshwater Research |volume=51 |issue=4 |pages=339–347|date=2000 |doi=10.1071/MF99125}}</ref>


==Human interactions==
==Human interactions==
The daggernose shark poses little danger to humans due to its small size and teeth.<ref name="compagno"/> This shark is caught in small numbers by [[artisan fishing|subsistence fishers]] in Trinidad, Guyana, Suriname, and French Guyana.<ref name="fowler et al"/> It also comprises about one-tenth of the catch of a northern Brazil [[gillnet|floating gillnet]] fishery targeting [[Serra Spanish mackerel]] (''Scomberomorus brasiliensis'') and [[Acoupa weakfish]] (''Cynoscion acoupa''), which operates in estuaries during the dry season. This shark is often found in markets, but is not highly regarded as a food fish. The [[International Union for Conservation of Nature]] (IUCN) has assessed this species as [[Critically Endangered]], as it has a limited distribution and is highly susceptible to [[overfishing]] due to its low reproductive rate. The daggernose shark has declined over 90% over the past decade off Brazil, and similar declines have likely also occurred elsewhere in its range as fishing pressure in the region continues to grow more intense. The IUCN has urgently recommended the implementation of conservation schemes and the expansion of fishery monitoring for this species.<ref name="iucn"/>
The daggernose shark poses little danger to humans due to its small size and teeth.<ref name="compagno"/> This shark is caught in small numbers by [[artisan fishing|subsistence fishers]] in Trinidad, Guyana, Suriname, and French Guiana.<ref name="fowler et al"/> It also comprises about one-tenth of the catch of a northern Brazil [[gillnet|floating gillnet]] fishery targeting [[Serra Spanish mackerel]] (''Scomberomorus brasiliensis'') and [[Acoupa weakfish]] (''Cynoscion acoupa''), which operates in estuaries during the dry season. This shark is often found in markets, but is not highly regarded as a food fish. The [[International Union for Conservation of Nature]] (IUCN) has assessed this species as [[Critically Endangered]], as it has a limited distribution and is highly susceptible to [[overfishing]] due to its low reproductive rate. The daggernose shark has declined over 90% over the past decade off Brazil, and similar declines have likely also occurred elsewhere in its range as fishing pressure in the region continues to grow more intense. The IUCN has urgently recommended the implementation of conservation schemes and the expansion of fishery monitoring for this species.<ref name="iucn status 19 November 2021" /> Evidence also points to this species being on the verge of or already in reproductive collapse.<ref name="blogs.scientificamerican.com"/>

==See also==
{{Portal|Sharks}}

*[[List of sharks]]


==References==
==References==
{{reflist|2}}
{{Reflist|25em}}


{{Carcharhinidae}}
{{Carcharhinidae}}
{{Taxonbar|from=Q942155}}


[[Category:Carcharhinidae]]
[[Category:Carcharhinidae|daggernose shark]]
[[Category:Fish of the Western Atlantic]]
[[Category:Marine fish of Brazil]]
[[Category:Fish of French Guiana]]
[[Category:Fish of Guyana]]
[[Category:Fish of Suriname]]
[[Category:Fish of Trinidad and Tobago]]
[[Category:Viviparous fish]]
[[Category:Viviparous fish]]
[[Category:Critically endangered fish]]

[[Category:Critically endangered biota of South America]]
[[ca:Isogomphodon oxyrhynchus]]
[[Category:Extant Eocene first appearances]]
[[de:Dolchnasenhai]]
[[Category:Fish described in 1839|daggernose shark]]
[[fr:Isogomphodon oxyrhynchus]]
[[Category:Taxa named by Johannes Peter Müller|daggernose shark]]
[[nl:Dolkneushaai]]
[[Category:Taxa named by Friedrich Gustav Jakob Henle|daggernose shark]]
[[ja:ツバクロザメ]]
[[ru:Остроносая акула]]

Latest revision as of 21:46, 28 October 2024

Not to be confused with the Goblin shark which has a similar snout.
Daggernose shark
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Order: Carcharhiniformes
Family: Carcharhinidae
Genus: Isogomphodon
T. N. Gill, 1862
Species:
I. oxyrhynchus
Binomial name
Isogomphodon oxyrhynchus
Range of the daggernose shark
Synonyms

Carcharias oxyrhynchus Müller & Henle, 1839

The daggernose shark (Isogomphodon oxyrhynchus) is a little-known species of requiem shark, in the family Carcharhinidae, and the only extant member of its genus. It inhabits shallow tropical waters off northeastern South America, from Trinidad to northern Brazil, favoring muddy habitats such as mangroves, estuaries, and river mouths, though it is intolerant of fresh water. A relatively small shark typically reaching 1.5 m (4.9 ft) in length, the daggernose shark is unmistakable for its elongated, flattened, and pointed snout, tiny eyes, and large paddle-shaped pectoral fins.

Daggernose sharks are predators of small schooling fishes. Its reproduction is viviparous, with females give birth to 2–8 pups every other year during the rainy season; this species is capable of shifting the timing of its reproductive cycle by several months in response to the environment. Harmless to humans, the daggernose shark is caught for food and as bycatch in artisanal and commercial fisheries. Limited in range and slow-reproducing, it has been assessed as Critically Endangered by International Union for Conservation of Nature in light of a steep population decline in recent years. The current population is believed to be extremely low, with no more than 250 individuals believed to be in existence as of 2023.[2] Indeed, it may even be in reproductive collapse, in which case it will likely become extinct in the near future.[3]

Taxonomy and phylogeny

[edit]
The illustration that accompanied Müller and Henle's original description.

The first scientific description of the daggernose shark, as Carcharias oxyrhynchus, was published by German biologists Johannes Peter Müller and Friedrich Gustav Jakob Henle in their 1839 Systematische Beschreibung der Plagiostomen. They chose the specific epithet oxyrhynchus, from the Greek oxys ("sharp" or "pointed") and rhynchos ("nose"). In 1862, American ichthyologist Theodore Gill coined the genius Isogomphodon for this species, from the Greek isos ("equal"), gomphos ("nail" or "peg"), and odous ("tooth"). However, Isogomphodon was subsequently relegated to being a synonym of Carcharhinus, until it was resurrected by shark authority Stewart Springer in 1950.[4] Regardless of its taxonomic validity, Isogomphodon, along with the genera Nasolamia and Prionace, is closely related to Carcharhinus. An extinct relative, I. acuarius, dates back to the Middle Eocene (45 Ma).[5]

Distribution and habitat

[edit]

The daggernose shark is found along the northeastern coast of South America, off Trinidad, Guyana, Suriname, French Guiana, and northern Brazil.[4] It reportedly occurs as far south as Valença in the central Brazilian state of Bahia, though fishery surveys have not detected this species in the area and it is apparently unknown to local fishermen.[1]

An inhabitant of coastal waters at a depth of 4–40 m (13–131 ft), the daggernose shark prefers highly turbid waters and decreases in number with increasing water clarity. Females tend to be found at greater depths than males.[6] Its range encompasses a wide continental shelf with a humid tropical climate, extensive mangroves, and draining by numerous rivers including the Amazon. Water salinity in this area ranges from 20 to 34 ppt, while the tidal amplitude can measure up to 7 m (23 ft).[1] Daggernose sharks are most common over shallow muddy banks and in estuaries and river mouths. It seems to be intolerant of low salinity, moving inshore during the dry season (June to November) and offshore during the rainy season (December to May).[7] This species is not known to make long-distance movements, though some local seasonal movements are possible.[1]

Description

[edit]
Ventral view of head.

As its common name suggests, the daggernose shark has a very long, flattened snout with a pointed tip and an acutely triangular profile from above. The eyes are circular and minute in size, with nictitating membranes (a protective third eyelid). The nostrils are small, without prominent nasal skin flaps. There are short but deep furrows at the corners of the mouth on both jaws. The tooth rows number 49–60 and 49–56 in the upper and lower jaws respectively. Each tooth has a single narrow, upright cusp; the upper teeth are slightly broader and flatter than the lower teeth, with serrated rather than smooth edges.[4]

The body is robustly built, with large, broad, paddle-like pectoral fins that originate under the fifth gill slit. The first dorsal fin originates over the posterior half of the pectoral fin bases. The second dorsal fin is about half as tall as the first and located over or slightly ahead of the anal fin. The anal fin is smaller than the second dorsal fin and has a deep notch in the rear margin. The caudal fin has a well-developed lower lobe and is preceded by a crescent-shaped notch on the upper side of the caudal peduncle. The coloration is a plain gray above, sometimes with a brownish or yellowish cast, and lighter below.[4] Males attain a length of 1.4 m (4.6 ft) and females 1.6 m (5.2 ft).[1] There are unsubstantiated records of individuals 2.0–2.4 m (6.6–7.9 ft) long.[4] The maximum known weight is 13 kg (29 lb).[6]

Biology and ecology

[edit]

The dominant shark species within the daggernose shark's range are the smalltail shark (Carcharhinus porosus) and the bonnethead (Sphyrna tiburo).[1] Its elongated snout and tiny eyes are likely consequences of living in murky sediment-laden waters, reflecting an adaptive emphasis on electroreception and other rostral senses rather than vision. The snout bears a superficial similarity to the goblin shark (Mitsukurina owstoni), some Apristurus catsharks, and the long-nosed chimaeras, all found in the deep sea.[6] With long jaws and numerous small teeth, the daggernose shark is well-suited for capturing the small schooling fishes that comprise most of its diet. Known prey taken include herring, anchovies, catfish, and croakers.[4]

The daggernose shark is viviparous; once the developing embryos exhaust their supply of yolk, the depleted yolk sac is converted into a placental connection through which the mother delivers sustenance. Females give birth to litters of 2–8 pups every other year, following a year-long gestation period. There is no correlation between female size and number of offspring.[6] Mating and parturition take place over a roughly six-month period from the beginning to the end of the rainy season. However, the daggernose shark is capable of shifting the timing of its reproductive cycle by at least four months, possibly in response to varying environmental conditions.[8] Females move into shallow coastal nurseries to give birth; one important nursery exists off Brazilian state of Maranhão.[6]

Newly born daggernose sharks measure 38–43 cm (15–17 in) in length.[6] Males mature at 103 cm (41 in) long, corresponding to an age of 5–6 years, while females mature at 115 cm (45 in) long, corresponding to an age of 6–7 years. The lifespan of males has been measured at up to 7 years, and females 12 years; extrapolating from growth rates suggest that the largest known males and females may be 12 and 20 years old respectively.[9]

Human interactions

[edit]

The daggernose shark poses little danger to humans due to its small size and teeth.[4] This shark is caught in small numbers by subsistence fishers in Trinidad, Guyana, Suriname, and French Guiana.[6] It also comprises about one-tenth of the catch of a northern Brazil floating gillnet fishery targeting Serra Spanish mackerel (Scomberomorus brasiliensis) and Acoupa weakfish (Cynoscion acoupa), which operates in estuaries during the dry season. This shark is often found in markets, but is not highly regarded as a food fish. The International Union for Conservation of Nature (IUCN) has assessed this species as Critically Endangered, as it has a limited distribution and is highly susceptible to overfishing due to its low reproductive rate. The daggernose shark has declined over 90% over the past decade off Brazil, and similar declines have likely also occurred elsewhere in its range as fishing pressure in the region continues to grow more intense. The IUCN has urgently recommended the implementation of conservation schemes and the expansion of fishery monitoring for this species.[1] Evidence also points to this species being on the verge of or already in reproductive collapse.[3]

See also

[edit]

References

[edit]
  1. ^ a b c d e f g Pollom, R.; Charvet, P.; Faria, V.; Herman, K.; Lasso-Alcalá, O.; Marcante, F.; Nunes, J.; Rincon, G.; Kyne, P.M. (2020). "Isogomphodon oxyrhynchus". IUCN Red List of Threatened Species. 2020: e.T60218A3094144. doi:10.2305/IUCN.UK.2020-3.RLTS.T60218A3094144.en. Retrieved 19 November 2021.
  2. ^ Lessa, Rosangela, et al. “Close to Extinction? The Collapse of the Endemic Daggernose Shark (Isogomphodon Oxyrhynchus) off Brazil.” Global Ecology and Conservation, vol. 7, 2016, pp. 70–81., doi:10.1016/j.gecco.2016.04.003.
  3. ^ a b "The Daggernose Shark is Near Extinction".
  4. ^ a b c d e f g Compagno, L.J.V. (1984). Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date. Rome: Food and Agricultural Organization. pp. 510–511. ISBN 92-5-101384-5.
  5. ^ Carrier, J.C.; J.A. Musick & M.R. Heithaus (2004). Biology of Sharks and Their Relatives. CRC Press. pp. 51–52. ISBN 0-8493-1514-X.
  6. ^ a b c d e f g Fowler, S.L.; R.D. Cavanagh; M. Camhi; G.H. Burgess; G.M. Cailliet; S.V. Fordham; C.A. Simpfendorfer & J.A. Musick (2005). Sharks, Rays and Chimaeras: The Status of the Chondrichthyan Fishes. International Union for Conservation of Nature and Natural Resources. pp. 306–308. ISBN 2-8317-0700-5.
  7. ^ Compagno, L.J.V.; M. Dando & S. Fowler (2005). Sharks of the World. Princeton University Press. p. 313. ISBN 978-0-691-12072-0.
  8. ^ Lessa, R.; F.M.Santana & P. Duarte-Neto (December 2006). "A critical appraisal of marginal increment analysis for assessing temporal periodicity in band formation among tropical sharks". Environmental Biology of Fishes. 77 (3–4): 309–315. Bibcode:2006EnvBF..77..309L. doi:10.1007/s10641-006-9111-7. S2CID 23735874.
  9. ^ Lessa, R.; F.M. Santana; V. Batista & Z. Almeida (2000). "Age and growth of the daggernose shark, Isogomphodon oxyrhynchus, from northern Brazil". Marine and Freshwater Research. 51 (4): 339–347. doi:10.1071/MF99125.
Retrieved from "https://en.wikipedia.org/enwiki/w/index.php?title=Daggernose_shark&oldid=1253986352"