Trophic ecology of an abundant predator and its relationship with fisheries

Abstract

Trophic studies are key components in animal ecology and fisheries research. Although stomach samples are often obtained from fisheries, diet studies that consider the influence of fisheries on dietary results are still lacking. Here, the diet of the draughtboard shark Cephaloscyllium laticeps, an abundant mesopredator in Tasmanian waters, was investigated. Stomach samples were obtained from gillnet and craypot fisheries sourced from 4 regions: central (100% gillnet), east coast (63% gillnet, 37% craypot), northwest (100% gillnet), and southwest Tasmania (100% craypot). Overall, C. laticeps consumed the same prey types in all regions, but the importance of some prey varied significantly between regions. Generalized linear models showed that region was the main factor affecting prey abundance in the diet. Fishing method had some influence on the abundance of some prey (crabs, octopus, and other molluscs (gastropods and bivalves)), but the effect of fishing method on pot-related species such as Jasus edwardsii (lobster) and octopus was not as prevalent as expected. The common occurrence of C. laticeps as a bycatch species and its high consumption of targeted fishery species (lobsters and octopus) indicates that C. laticeps has a strong interaction with the fisheries. Therefore, the relationship between these fishery species and C. laticeps should be considered in food web studies in Tasmanian waters.Fil: Barnett, Adam. Deakin University. School Of Life And Environmental Sciences; Australia. James Cook University. School of Marine and Tropical Biology. Estuary and Tidal Wetland Ecosystems Research Group. Centre for Tropical Water & Aquatic Ecosystem Research; Australia. OceansIQ; AustraliaFil: Yick, Jonah L.. Inland Fisheries Service; AustraliaFil: Abrantes, Kátya G.. James Cook University. School of Marine and Tropical Biology. Estuary and Tidal Wetland Ecosystems Research Group. Centre for Tropical Water & Aquatic Ecosystem Research; AustraliaFil: Awruch, Cynthia Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina. University of Tasmania. School of Zoology; Australi

Predation Risk within Fishing Gear and Implications for South Australian Rock Lobster Fisheries

“…conger eels, [ 10 ]), elasmobranchs (e.g. catsharks,[ 11 ]), and cephalopods (e.g. octopus, [ 12 , 13 ]) are common middle-trophic predators within fishing gear.…”

Biology of the New Zealand carpet shark Cephaloscyllium isabellum (Scyliorhinidae)

“…It is possible that the fishery discards component of the diet was underestimated as some of the identified fish prey (e.g., rattails, jack mackerel, bellowsfish) may have been previously caught in fishing operations but discarded whole. However, relatively fast-swimming semi-pelagic species (e.g., jack mackerels, pilchards, barracouta) were recorded in the diets of C. umbratile (Taniuchi, 1988) and C. laticeps (Barnett et al, 2013). The presence of squid and some semi-pelagic teleosts in the C. isabellum diet suggests some feeding above the bottom using short bursts of speed or ambush tactics.…”

“…That species had a diet dominated numerically by fish (agnathans 2%, elasmobranchs 8%, and teleosts 70%) and cephalopods (14%), with a minor component of crustaceans (6%). An extensive study of the Australian swell shark C. laticeps found a diet of crustaceans (29%, primarily the rock lobster Jasus edwardsii and Paguridae), fish (29%, mainly demersal species), cephalopods (25%, mainly octopus), and shelled molluscs (16%) (Barnett et al, 2013). Bass et al, (1975) reported that the South African balloon shark C. sufflans fed on open sandy or mud bottoms, primarily consuming crustaceans and cephalopods, but also teleosts and elasmobranchs.…”

“…It is likely that egg cases of C. isabellum are attacked and the contents consumed by carnivorous gastropods, as recorded for other oviparous elasmobranch species (Grover, 1972;Cox and Koob, 1973). Elasmobranch egg cases have also been recorded in stomachs of New Zealand teleosts (e.g., Horn et al, 2012); Barnett et al (2013) recorded cannibalism of egg cases by C. laticeps. Cannibalism on juveniles was reported for both C. umbratile and C. laticeps (Taniuchi, 1988;Barnett et al, 2013), but was not found for C. isabellum in the current work.…”

“…Elasmobranch egg cases have also been recorded in stomachs of New Zealand teleosts (e.g., Horn et al, 2012); Barnett et al (2013) recorded cannibalism of egg cases by C. laticeps. Cannibalism on juveniles was reported for both C. umbratile and C. laticeps (Taniuchi, 1988;Barnett et al, 2013), but was not found for C. isabellum in the current work. Juvenile elasmobranchs (particularly Squalus acanthias) occurred in the C. isabellum diet, however, so a larger sample of stomachs might also demonstrate cannibalism in this species.…”