Stress, survival and movement following fishing gear capture in chondrichthyan species
2017-10-02T23:04:59Z (GMT) by
Fishing procedures involve capture in fishing gear, subsequent handling and exposure to air (for discarded animals), which can cause physical damage, asphyxiation, stress, physiological changes and lead to mortality, depending on the magnitude of the stress. The first objective of the present study was to investigate the effects of fishing (capture, handling and air exposure) on a target, byproduct (retained non-targeted) and bycatch (discarded) species of Australian chondrichthyans, and assess their post-release survival or mortality. The target and byproduct species were gummy shark (Mustelus antarcticus) and elephant fish (Callorhinchus milii), and the bycatch species was southern fiddler ray (Trygonorrhina dumerilii). Capture in different fishing gears for various periods was simulated under laboratory conditions and physiological changes were measured through repeated blood sampling. The animals’ post-release fate was determined in captivity during a 72-h blood monitoring period for all species and in the wild for gummy sharks and southern fiddler rays tagged with acoustic transmitters. The acoustic monitoring data gained with telemetry was also used to investigate these species’ movement patterns, habitat use and long-term fate inside Port Phillip Bay and Swan Bay Marine Park, which are natural habitats for the gummy shark and southern fiddler ray populations (neonate, juvenile and adult animals). This was the second objective of the present study. <br> The results showed that capture stress and handling caused physiological changes in all three species. Increases in plasma lactate and potassium levels and decreases in plasma glucose levels were recorded in stressed elephant fish. Increases in plasma lactate, glucose and potassium levels were measured in stressed gummy sharks. Elevated plasma lactate and glucose levels were recorded in stressed southern fiddler rays. The blood variables measured immediately after capture did not show the extent of the physiological responses to capture stress in elephant fish and gummy sharks. However, plasma lactate levels in southern fiddler rays peaked immediately after capture and capture with air exposure. Gillnet was the capture gear causing the greatest stress and mortality in elephant fish and gummy sharks. Trawl capture caused greatest stress in southern fiddler rays, and air exposure immediately after trawl capture significantly exacerbated stress-related physiological changes. Handling alone significantly increased plasma lactate concentrations in elephant fish and gummy sharks, but not in southern fiddler rays. Stress from capture, handling and transport significantly increased blood variable levels and caused irregular short-term movement activities and reduced area use of three stressed gummy sharks and three stressed southern fiddler rays tagged with transmitters and released to the wild. Irregular movement may have increased the chances of two of these gummy sharks being subsequently recaptured by fishers. Mean area use was not statistically different between control treatments and capture treatments during the short-term movement for gummy sharks and southern fiddler rays. Immediate mortality of elephant fish and gummy shark after capture stress in all gears overall was 0% and 3%, respectively, and delayed mortality of these species was 25% and 6%, respectively. No immediate or delayed mortality after stress was recorded in southern fiddler rays. These post-release survival results suggest that elephant fish have high sensitivity to capture-stress in fishing gear, gummy sharks have medium sensitivity and southern fiddler rays have low sensitivity (resilient) to capture-stress in fishing gear. <br> Long-term movement patterns and area use varied among gummy sharks and southern fiddler rays. Gummy sharks used larger areas inside Port Phillip Bay and Swan Bay than southern fiddler rays. In general, slightly higher movement and larger area use occurred at night than during the day for both species, but the differences were not significant. Both species used the Swan Bay Marine Park, with the gummy sharks using larger areas inside the marine park than the southern fiddler rays; however, the rays stayed inside the marine park for longer periods than the gummy sharks. The greatest use areas for gummy sharks were in the north-western and far southern regions of the marine park, sharing the latter with the southern fiddler rays. Gummy sharks preferred sparse seagrass (Zostera and Heterozostera) with associated filamentous algae inside Swan Bay followed by macroalgae habitat type. Bare sediment was the habitat type more used inside Swan Bay for southern fiddler rays followed by medium seagrass (Zostera and Heterozostera) with associated filamentous algae. No differences in movement patterns, area use and day and night activities between sexes were observed in gummy sharks and southern fiddler rays. <br> The present study provides important physiological, mortality and movement information for ecological risk assessments from effects of fishing of these three chondrichthyan species (elephant fish, gummy shark and southern fiddler ray), aiming to improve management and conservation of their populations. The study demonstrates that the use of stress-related physiological changes and acoustic monitoring together is highly effective for quantifying immediate and delayed mortality caused by fishing capture and irregular short-term movement patterns after capture. Because blood samples taken immediately after capture and landing on boats may not show the extent of the stress-related physiological changes, delayed mortality estimates solely from one blood sample can be underestimated. Therefore tagging with acoustic transmitters and release provides supporting information to determine delayed mortality, area use and movement patterns. The combination of these two approaches, physiological changes and acoustic monitoring, can facilitate studies undertaken on boats when animals cannot be held in tanks or pens following capture to determine their post-release survival.