Gillnet Capture Research Articles

Stress related physiological changes and post-release survival of Port Jackson sharks ( Heterodontus portusjacksoni) and gummy sharks ( Mustelus antarcticus) following gill-net and longline capture in captivity

Information on effects of fisheries capture on the physiology and post-release condition of sharks is urgently needed to design and implement effective fisheries management plans for shark stocks around the world, but obtaining data on post-release condition in the wild is very difficult. We used a controlled setting to subject Port Jackson sharks ( Heterodontus portusjacksoni) and gummy sharks ( Mustelus antarcticus) to varying durations of gill-net and longline capture stress for up to 360 min and monitored their condition via repeated blood sampling during a subsequent 72-h recovery period. Changes in plasma metabolites and electrolytes of Port Jackson sharks in response to our experimental treatment were small and no mortality was observed, suggesting that Port Jackson sharks are resilient to capture stress. In contrast, gummy sharks reacted very sensitively to capture stress, with severely disrupted acid–base and electrolyte balances, and immediate and delayed mortality was substantial (up to 70%) following gill-net capture. Moribund gummy sharks had very high plasma concentrations of lactate and potassium. Management measures for shark species that are susceptible to capture stress should aim to reduce the probability of interactions of that species with fishing gear.

Spiny Dogfish Mortality Induced by Gill-Net and Trawl Capture and Tag and Release

Abstract The spiny dogfish Squalus acanthias was once classified as an underutilized species along the U.S. East Coast, but it constituted a lucrative fishery in the 1990s until recruitment overfishing caused stock collapse. Coastwide restrictions currently apply; federal stock assessment models use bycatch mortality estimates of 50% for trawling, 75% for gill netting, and 100% for hook-and-line fishing. This study examined mortality at the southern end of commercial fishing operations caused by trawling for 30- and 90-min periods and by gill nets of various mesh sizes set for 19- to 24-h periods. Both experiments used tagged and untagged fish placed in rectangular cages anchored to the seafloor for 48 h. Tags were the Floy SS-94 single-barb nylon dart with a stainless steel wire insert. A total of 635 spiny dogfish were captured by trawl and all were alive, for a 0% initial mortality rate. A total of 2,284 spiny dogfish were collected by gill net for an initial mortality rate of 17.5%. There was no addit...

Serological Changes Associated with Gill-Net Capture and Restraint in Three Species of Sharks

Abstract To investigate the biochemical effects of capture and restraint on sharks, 17 serum constituents were measured in three species (bonnethead shark Sphyrna tiburo, blacktip shark Carcharhinus limbatus, and bull shark C. leucas) after gill-net capture. The relative degree of capture effects on each animal was judged using an index of behavioral response devised for use in tag−recapture studies. Serum from each shark was assayed for glucose, creatinine, uric acid, sodium, chloride, potassium, inorganic phosphate, total and ionized calcium, total protein, albumin, globulin, alkaline phosphatase, lactate, lactate dehydrogenase, aspartate aminotransferase, and total iron. In addition, hematocrit was measured from whole blood for each shark. When correlated with the relative degree of capture effects, there were significant intraspecific changes in the concentration of potassium, lactate, inorganic phosphate, uric acid, alkaline phosphatase, aspartate aminotransferase, total and ionized calcium, and gluc...

Behaviour of gill-net and rod-captured Atlantic salmon ( Salmo salar L.) during upstream migration and following radio tagging

The behaviour of radio-tagged Atlantic salmon ( Salmo salar L.) was studied in the River Ohcejohka in subarctic Finland. The objective was to determine the effects of gill-net entanglement and catch and release angling on the behaviour of upstream migrating salmon. 23 grilse and one 2 sea-winter (SW) salmon were tagged with radio transmitters and some were tracked for a period of over 3 months. Gill-net caught fish exhibited extensive downstream running, presumably caused by stress from capture and tagging. Post-tagging downstream movement in rod-caught salmon was also observed, but was not as extensive. Upstream migration was delayed in all tagged fish. The results of this study suggest that gill-net capture negatively impacts the upstream migration behaviour of Atlantic salmon and that the negative effects of capture and radio tagging can well exceed those proposed in current literature.

Habitat Use and Movements of Shortnose and Atlantic Sturgeons in the Lower Cape Fear River, North Carolina

Abstract We conducted a gill-net survey and used sonic tracking to document the distribution and movements of adult shortnose sturgeons Acipenser brevirostrum and juvenile Atlantic sturgeons Acipenser oxyrhynchus in the lower Cape Fear River, North Carolina. Shortnose sturgeons were rare; only eight fish were captured from 1990 to 1993. The five fish we tracked occupied river kilometer 16–96 from early January to May. The presence of gravid females and the rapid (11.5–27.0 km/d), directed upstream migrations we observed provided evidence that shortnose sturgeons may attempt to reproduce in this drainage. We also documented the disruption of spawning migrations by dams and incidental gill-net capture, which may prevent these fish from ever reaching their spawning grounds. Atlantic sturgeon juveniles were relatively common and preferred deep areas (>10 m) in the vicinity of the saltwater–freshwater interface (km 46). In summer they held position for extended periods and apparently fasted, but were more acti...

External scarring of whitefish, Coregonus nasus and C. clupeaformis complex, from the western Northwest Territories, Canada

Up to 40% of whitefish (Coregonus nasus and C. clupeaformis) sampled during spawning migrations from the area of the Mackenzie Delta, N.W.T., had external scars. Percent frequency of scarred individuals varied geographically from the Mackenzie mainstem and tributaries, where 20% were scarred, to Anderson river (2%), Cox Lake (16%), and Alaska (0–7%). Within the Mackenzie system fish captured at mainstem locations had approximately twice the frequency of scarring than did fish from tributary locations. Scars were classified as either slash or round type. Both scar types were located more frequently on the left side of the fishes and below the lateral line. Details of orientation and location on the body provided clues permitting the assignment of putative causation. Small round scars were restricted to locations with connections to the Arctic Ocean and were probably caused by the marine parasitic copepod Coregonicola or by Arctic lampreys (Lampetra japonica). Larger round scars were either the result of attacks by lampreys or by previous gill net capture. Unequal distribution and orientation on the body of slash scars indicated previous capture in gill nets or predation attempts by bears, birds, or piscivorous fishes.