Age structures and reproductive patterns of two species of sea snake, Lapemis hardwickii Grey (1836) and Hydrophis elegans (Grey 1842), incidentally captured by prawn trawlers in northern Australia

2001 ◽  
Vol 52 (2) ◽  
pp. 193 ◽  
Author(s):  
T. M. Ward
Keyword(s):  
Sexual Maturity ◽  
Ecological Effects ◽  
Northern Australia ◽  
Sea Snake ◽  
Reproductive Patterns ◽  
Sea Snakes ◽  
By Catch ◽  
Reproductive Cycles ◽  
Age Structures

Lapemis hardwickiiand Hydrophis elegans caught by prawn trawlers reach at least 6.7 and 8.9 years of age respectively.Most L.hardwickii sampled were 2—4 years of age,and most H.elegans were 3—5 years of age. Female L.hardwickii and H.elegans appear to reach sexual maturity after 2 years and minimum snout—vent lengths of approximately 76 and 120 cm respectively.The reproductive cycles of L.hardwickii and H.elegans are similar:mating occurs between early May and the end of July;ovulation during August —September;and gestation during September—December and September—February respectively.L.hardwickii and H.elegans produce approximately 8.5 and 12.7 offspring per clutch respectively.However,female L.hardwickii breed annually whereas female H.elegans only breed every 2—3 years.The mean annual reproductive outputs of L. hardwickii (8.4 offspring per year)and H.elegans (7.5)are thus similar. Sea snakes appear to be less fecund and more susceptible to trawler-induced effects than most by-catch taxa,and should be a focus of future strategies to ameliorate the ecological effects of prawn trawling in northern Australia.

Hydrophis donaldi (Elapidae, Hydrophiinae), a highly distinctive new species of sea snake from northern Australia

Zootaxa ◽  
2012 ◽  
Vol 3201 (1) ◽  
pp. 45 ◽  
Author(s):  
KANISHKA D.B. UKUWELA ◽  
KATE L. SANDERS ◽  
BRYAN G. FRY
Keyword(s):  
New Species ◽  
Habitat Preferences ◽  
The Body ◽  
Colour Pattern ◽  
Northern Australia ◽  
Nucleotide Substitutions ◽  
Sea Snake ◽  
Sea Snakes ◽  
Morphological Diagnosis ◽  
By Catch

A new species of viviparous sea snake, Hydrophis donaldi sp. nov. (Hydrophiinae), is described from the Gulf of Carpen-taria, northern Australia. Molecular analyses reveal this species as a deeply divergent lineage within the Hydrophis sub-group, and separate it from all other sampled taxa by fixed nucleotide substitutions at three independent mitochondrial andnuclear loci. The new species is assigned to Hydrophis based on the current morphological diagnosis of this large but pa-raphyletic genus, and is distinguished from all other Hydrophis species and closely allied genera by a combination of mor-phological characters relating to scalation, colour pattern and osteology. Using current keys for sea snakes, H. donaldi sp.nov. might be mistaken for H. coggeri, H. sibauensis or H. torquatus diadema but it is readily distinguished from thesespecies by a higher number of bands on the body and tail, lower ventral count, strongly spinous body scales, and a wider,more rounded head. Sea snakes have been sampled intensively in the Gulf of Carpentaria due to their vulnerability to by-catch in the region’s commercial prawn-trawl fisheries. That this highly distinctive new species has evaded discovery inthe region until now is surprising, but might be explained by its habitat preferences. All known specimens of H. donaldi sp. nov. were found in estuarine habitats that are relatively poorly surveyed and are not targeted by commercial fisheries.

Growth, sexual dimorphism, and population biology of the olive sea snake, Aipysurus laevis, on the Great Barrier Reef of Australia

2000 ◽  
Vol 21 (3) ◽  
pp. 289-300 ◽  
Author(s):  
Glen Burns ◽  
Harold Heatwole
Keyword(s):  
Sexual Dimorphism ◽  
Great Barrier Reef ◽  
Population Biology ◽  
Sexual Maturity ◽  
Reproductive Behaviour ◽  
Barrier Reef ◽  
Sea Snake ◽  
Sea Snakes ◽  
Equivalent Length ◽  
Reef Edge

AbstractThe olive sea snake, Aipysurus laevis (Lacépède) grows at a rate of 0.22-0.95 cm/month, with young animals growing faster than older ones. Males reach sexual maturity in their third year and females in their fourth or fifth year. There is sexual dimorphism in size, with females larger than males; at snout-vent lengths greater than 80 cm, females are heavier than males of equivalent length. Small snakes were uncommon. Apparent sexratio favours males in winter but moves toward equality or even a preponderance of females in summer, probably reflecting changes in reproductive behaviour. Numbers of snakes are approximately 0.70-0.86 snakes per metre of reef edge. Olive sea snakes live to about 15 years or older.

Sea snake by-catch of fish trawlers on the northern Australian continental shelf

1996 ◽  
Vol 47 (4) ◽  
pp. 625 ◽  
Author(s):  
TM Ward
Keyword(s):  
Continental Shelf ◽  
Absolute Abundance ◽  
Sea Snake ◽  
North West ◽  
The North ◽  
Sea Snakes ◽  
Exponential Decline ◽  
Arafura Sea ◽  
By Catch ◽  
Trawl Surveys

During 1986-90, 206 sea snakes were collected from Taiwanese pair-trawlers (North West Shelf, 1986-87), Thai stern-trawlers (Arafura Sea, 1986-87), RV Soela (North West Shelf, 1986) and RV Clipper Bird (Timor and Arafura Seas, 1990). Taiwanese (58 specimens; 294.8 h trawled) and Thai (71 specimens; 1244 h trawled) vessels trawled in 50-75 m and caught 10 and 7 species respectively. The Soela (41 specimens; 72.5 h trawled) and Clipper Bird (36 specimens; 103 h trawled) operated in depths of 19-198 m and each caught 12 species. Hydrophines (10 species plus one specimen from an undescribed taxon) represented 68.4% of the specimens. Aipysurines (6 species) were more common in samples from the North West Shelf (46.2% of taxa, 56.6% of specimens) than from the Timor and Arafura Seas (28.6% of taxa, 11.2% of specimens). Taiwanese boats on the North West Shelf (1980-90) and Thai boats in the Arafura Sea (1985-90) were estimated to have caught 49000 (� 5600) and 10000 (� 1250) sea snakes respectively. Trawl surveys (e.g. Soela and Clipper Bird) may be unsuitable for monitoring sea snakes, because approximately 25 surveys would be needed to detect a 20% exponential decline in absolute abundance.

Reducing impacts of trawling on protected sea snakes: by-catch reduction devices improve escapement and survival

2009 ◽  
Vol 60 (8) ◽  
pp. 824 ◽  
Author(s):  
David A. Milton ◽  
Gary C. Fry ◽  
Quinton Dell
Keyword(s):  
Crew Member ◽  
Western Pacific ◽  
Small Fish ◽  
Separate Study ◽  
Sea Snake ◽  
Fishing Season ◽  
Sea Snakes ◽  
Paired Control ◽  
By Catch ◽  
Northern Prawn Fishery

Sea snakes (Hydrophidae) are by-catch of prawn trawling throughout the tropical Indo-western Pacific. We tested the effectiveness of three by-catch reduction device (BRD) types set at different distances from the codend in Australia’s Northern Prawn Fishery (NPF). Trained crew-member observers compared the numbers of sea snakes caught in paired Control and Treatment nets in 1365 trawls. Catches of sea snakes were reduced by 43% on those vessels where a Fisheye BRD was positioned less than 70 meshes from the codend. A separate study with a scientific observer undertook trials with a ‘popeye’ Fishbox BRD. This BRD reduced sea snake catch by 85% and small fish by-catch by 48%. Catches of target prawn were similar for all nets in both studies (difference <2%). Adoption of the more effective BRDs (‘popeye’ Fishbox or Fisheye BRDs) by the NPF and locating them within 70 meshes of the codend can potentially reduce sea snake catch and thus their mortality from ~7000 in the 2007 fishing season to as few as 1500 snakes. Our study shows that the use of BRDs in tropical coastal demersal fisheries and positioning them closer to the codend will greatly reduce the catch of vulnerable sea snakes.

Factors affecting the catch rates and relative abundance of sea snakes in the by-catch of trawlers targeting tiger and endeavour prawns on the northern Australian continental shelf

2000 ◽  
Vol 51 (2) ◽  
pp. 155 ◽  
Author(s):  
T. M. Ward
Keyword(s):  
Continental Shelf ◽  
Relative Abundance ◽  
Sampling Effort ◽  
Sea Snake ◽  
Factors Affecting ◽  
Sea Snakes ◽  
The Status ◽  
By Catch ◽  
Catch Rates ◽  
Northern Prawn Fishery

A total of 4378 sea snakes (14 species; 5 unidentified specimens) were collected from 21 082 h of sampling effort by trawlers of the Northern Prawn Fishery. Most species (12) were collected from the southern Gulf of Carpentaria. Hydrophis elegans and Disteira major were caught frequently in all areas. The catch rates of H. elegans and Lapemis hardwickii were highest in the eastern gulf and in depths of 31–40 and <20 m respectively. Hydrophis elegans represented >27% of specimens from most areas. Other species that represented ≥20% of specimens from one or more areas were: L. hardwickii, H. ornatus, D. major and Aipysurus eydouxii. Catch rates of all species of snakes combined did not differ significantly between 1984–86 and 1989–90, and were moderately high around Groote Eylandt where the fishery is centred. Most by-catch species occur in areas that are not subjected to extensive trawling, and there are no data to suggest that this fishery seriously threatens any population of sea snake. However, sea snakes may be more vulnerable to trawler-induced effects than most other by-catch species, and formal assessment of the status of populations is needed.

Sea snake by-catch of prawn trawlers on the northern Australian continental shelf

1996 ◽  
Vol 47 (4) ◽  
pp. 631 ◽  
Author(s):  
TM Ward
Keyword(s):  
Data Collection ◽  
Continental Shelf ◽  
Total Catch ◽  
Sea Snake ◽  
Sea Snakes ◽  
Cape York ◽  
By Catch ◽  
Penaeus Merguiensis ◽  
Northern Prawn Fishery

This paper describes and compares the sea snakes caught by vessels that target tiger prawns and endeavour prawns or that target the banana prawns Penaeus merguiensis and P. indicus. In 1989-90, 5203 sea snakes (14 species; 7 unidentified specimens) were purchased from fishers who trawled between Koolan Island and Cape York and participated in a dedicated carcass-tagging and data-collection programme. Hydrophines (11 species) represented 86.7% of the total catch. Aipysurines (3 species) represented 15.0% of specimens from vessels that targeted tiger prawns or endeavour prawns, but only 1.1% of specimens from vessels that targeted the banana prawns P. merguiensis and P. indicus. Prawn trawlers that operated between Koolan Island and Cape York during 1990 caught approximately 81 080 (� 13 670) sea snakes. Vessels that targeted tiger/endeavour prawns, P. merguiensis and P. indicus caught approximately 69260 (� 8750), 7200 (� 3250) and 4620 (� 1120) sea snakes respectively. The results emphasize the advantages of interactions between fishers and scientists and the need to assess separately the impacts of the three fisheries that constitute the northern prawn fishery.

The reproductive biology and diet of sea snake bycatch of prawn trawling in northern Australia: characteristics important for assessing the impacts on populations

2001 ◽  
Vol 7 (1) ◽  
pp. 55 ◽  
Author(s):  
G. C. Fry ◽  
D. A. Milton ◽  
T. J. Wassenberg
Keyword(s):  
Benthic Fish ◽  
Northern Australia ◽  
Sea Snake ◽  
Pregnant Females ◽  
Sea Snakes ◽  
Catch Up ◽  
Specialized Diet ◽  
Trawl Catches ◽  
Northern Prawn Fishery ◽  
Closed Season

Trawlers catch up to 17 species of sea snake as bycatch in the Northern Prawn Fishery (NPF) in northern Australia. We examined the biological characteristics of 660 sea snakes caught by research, scientific observer and commercial vessels between 1986 and 1998 as part of a project to assess their vulnerability. Three species accounted for more than 75% of the total sea snakes caught. Hydrophis species were more common in unstructured habitats close to prawn trawling grounds, while Aipysurus species were the dominant species in areas having reef structure. Sea snakes were caught more frequently at night on commercial trawlers and even more were caught during the day by research trawling. Female sea snakes were caught more often than males for 10 out of 13 species examined. The proportion of mature sea snakes in trawl catches was high (67% males, 89% females). Juvenile sea snakes of most species are not caught suggesting there is little impact of trawling on recruits. We found all species breed annually, producing a few large young after a gestation period of 6-7 months. Litter size varied between 1 to 20 and young of most species were born during the NPF closed season (Nov-Mar). Except for Aipysurus duboisii, Disteira major and Hydrophis ornatus, pregnant females of most species were not more catchable by prawn trawls than non-pregnant females. The relative clutch mass had little effect on the catchability of pregnant females. Most sea snake species had a specialized diet, feeding on one to four benthic fish species and did not appear to be attracted into trawl grounds by the increased availability of discarded bycatch. Their reproductive characteristics mean that populations of many species caught by trawlers in northern Australia are potentially vulnerable.

Incidental capture of sea-snakes (Hydrophiidae) by prawn trawlers in the Gulf of Carpentaria, Australia

1994 ◽  
Vol 45 (3) ◽  
pp. 429 ◽  
Author(s):  
TJ Wassenberg ◽  
JP Salini ◽  
H Heatwole ◽  
JD Kerr
Keyword(s):  
Survival Rate ◽  
Coastal Waters ◽  
Significant Interaction ◽  
Catch Per Unit Effort ◽  
Sea Snake ◽  
Incidental Capture ◽  
Seasonal Movement ◽  
Sea Snakes ◽  
Breeding Cycles ◽  
Shallow Coastal Waters

Sea-snakes were collected from research trawlers and commercial prawn trawlers in the Gulf of Carpentaria during the period from April 1976 to December 1991. The data were analysed on the basis of CPUE (catch per unit effort) for depth, latitude and season. The research trawlers, operating in the eastern Gulf of Carpentaria, and the commercial prawn trawlers, operating in the south-western Gulf of Carpentaria, caught sea-snakes at a rate of 0.028 and 0.026 sea-snakes per metre of headrope length per hour, respectively. Lapemis hardwickii was the sea-snake most commonly caught by the research trawlers-53% of all snakes-and Hydrophis elegans was the sea-snake most commonly caught by commercial trawlers-25% of all snakes. Depth was the most significant factor affecting CPUE, with more than 70% of all sea-snakes being caught in waters less than 15 m deep. When catches of all species were combined, a significant interaction (P<0.05) existed between depth and season. L. hardwickii specimens were caught more frequently in shallow coastal waters (< 15 m deep) in spring but in deeper water further offshore in autumn. A significant interaction between latitude and depth was found for Astrotia stokesii; specimens were caught more frequently in deeper water at 14% Enhydrina schistosa is generally coastal, with 8800 of specimens being caught in water less than 10 m deep. Seasonal movement of sea-snakes between inshore and offshore waters may be linked to their breeding cycles. The estimated number of sea-snakes captured in the Gulf of Carpentaria for the 1991 prawning season ranged from 73 583 to 165 559, with a mean of 119 571. The survival rate of sea-snakes from commercial prawn trawls was about 60% and hence between 29 801 and 67 051 sea-snakes are estimated to have died.

Reproductive biology of two sympatric colubrid snakes, Chironius flavolineatus and Chironius quadricarinatus, from the Brazilian Cerrado domain

2010 ◽  
Vol 31 (4) ◽  
pp. 463-473 ◽  
Author(s):  
Roberta Richard Pinto ◽  
Otavio Augusto Vuolo Marques ◽  
Ronaldo Fernandes
Keyword(s):  
Reproductive Biology ◽  
Sexual Maturity ◽  
Egg Production ◽  
Sympatric Species ◽  
Egg Laying ◽  
Reproductive Pattern ◽  
Brazilian Cerrado ◽  
Wet Season ◽  
Reproductive Cycles ◽  
First Time

AbstractThe reproductive biology of Chironius flavolineatus and C. quadricarinatus from the Brazilian Cerrado domain is described, including sexual maturity, female fecundity, and reproductive cycles of males and females. Egg-laying is recorded here for the first time for C. quadricarinatus. Males of both species attain sexual maturity with a smaller snout-vent length than females. Females of C. flavolineatus have an extended reproductive cycle with egg production during the wet season, whereas males exhibit year-round sperm production. Chironius quadricarinatus has continuous reproductive cycles in both sexes. Differences in reproductive pattern between these two sympatric species are probably related to phylogenetic constraints on intrageneric lineages of Chironius.

scholarly journals Novel vascular plexus in the head of a sea snake (Elapidae, Hydrophiinae) revealed by high-resolution computed tomography and histology

2019 ◽  
Vol 6 (9) ◽  
pp. 191099 ◽  
Author(s):  
Alessandro Palci ◽  
Roger S. Seymour ◽  
Cao Van Nguyen ◽  
Mark N. Hutchinson ◽  
Michael S. Y. Lee ◽  
...  
Keyword(s):  
Parietal Bone ◽  
Vascular Network ◽  
Low Oxygen ◽  
High Resolution Computed Tomography ◽  
Sea Snake ◽  
Sea Snakes ◽  
Arterial Blood ◽  
Large Vein ◽  
Microct Imaging ◽  
The Brain

Novel phenotypes are often linked to major ecological transitions during evolution. Here, we describe for the first time an unusual network of large blood vessels in the head of the sea snake Hydrophis cyanocinctus . MicroCT imaging and histology reveal an intricate modified cephalic vascular network (MCVN) that underlies a broad area of skin between the snout and the roof of the head. It is mostly composed of large veins and sinuses and converges posterodorsally into a large vein (sometimes paired) that penetrates the skull through the parietal bone. Endocranially, this blood vessel leads into the dorsal cerebral sinus, and from there, a pair of large veins depart ventrally to enter the brain. We compare the condition observed in H. cyanocinctus with that of other elapids and discuss the possible functions of this unusual vascular network. Sea snakes have low oxygen partial pressure in their arterial blood that facilitates cutaneous respiration, potentially limiting the availability of oxygen to the brain. We conclude that this novel vascular structure draining directly to the brain is a further elaboration of the sea snakes' cutaneous respiratory anatomy, the most likely function of which is to provide the brain with an additional supply of oxygen.

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