Survival Of Released Flathead

[Dreamtime]

2004/071 National strategy for the survival of released line caught fish: maximising post- release survival in line caught flathead taken in sheltered coastal waters

OBJECTIVES:

Estimate post-release survival (PRS) rates for key flathead species associated with current hook and line fishing practices.

Evaluate the suitability of circle and non-traditional hooks in terms of enhancing PRS and minimising hooking damage.

Based on objectives 1 and 2 develop protocols that can be readily applied to maximize PRS in flathead.

NON TECHNICAL SUMMARY:

Flathead represent the largest catch of any fish group taken by recreational fishers in Australia and, after bream, account for the greatest numbers of fish released by recreational fishers (National Recreational Fishing Survey). Flathead are taken around Australia, with catches concentrated in the eastern states, including Tasmania. Sand flathead (Platycephalus bassensis) is the dominant species taken in estuarine and sheltered inshore waters of Tasmania and Victoria whereas dusky flathead (P. fuscus) is the main species taken from NSW and southern Queensland. Legal minimum size and bag limits apply for flathead, though there is little consistency between jurisdictions.

A review of post-release survival (PRS) in line caught fish (McLeay et al. 2002) identified flathead as a priority group, with research to focus on the effects of handling and hook damage on survival. The present study represents a component of the National Strategy for the Survival of Released Line Caught Fish.

The principal objectives of this study were to estimate the short-term post-release survival rates for sand and dusky flathead, and to determine whether there was any survival benefit in the use of circle hooks rather than conventional hook patterns. Recognising the increasing uptake of lures (especially soft plastics) for flathead, the potential impact of their use on post- release survival was also assessed. Using the results of this research we have been able to develop protocols that can be readily applied by recreational fishers to maximise the survival of flathead.

The study involved experiments in which flathead (sand flathead in Tasmania and dusky flathead in southern Queensland) were captured by angling and then held in aquaria for several days to assess short-term survival. In addition, catch rates and hooking locations for a Non-technical summary range of hook types were compared. Volunteer anglers also provided hooking information for flathead captured using bait and lure fishing methods.

Anatomical hooking location was determined to be the major factor contributing to mortality in flathead. Fish hooked in the throat or gut (deep-hooked) suffered greater mortality than those hooked in the lip or mouth (shallow-hooked). The short-term survival rate for shallow- hooked fish was almost 100% for sand flathead and 96% for dusky flathead, whereas survival rates for deep-hooked fish were significantly lower, around 64% for sand flathead and 73% for dusky flathead.

Mortality in deep-hooked fish was generally associated with injuries to vital organs (gills, heart, liver) and survival was lower if bleeding was associated with the hooking injury. For sand flathead the odds of survival for deep-hooked fish were eight times greater for non- bleeders. Data for dusky flathead were limited but also exhibited a trend towards lower survival rates in bleeders.

Cutting line rather than removing the hook can increase survivorship in deep-hooked fish. Although survival rates for deep-hooked sand flathead were higher for hook left in (81%) than for hook removed (60%), differences were not significant, reflecting the small sample sizes involved. Very limited data were available for dusky flathead so the impact of cutting the line on survival could not be assessed reliably. We did observe evidence that some survivors (both species) expelled hooks within a short time after capture. Despite the absence of definitive evidence of the benefits of cutting the line in gut-hooked flathead we conclude that the practice should be promoted.

Besides hooking location, the only other factor significantly implicated in the survival of dusky flathead was ‘surface interval’ – the time period between capture and placement of the fish in the experimental tanks. During this period the fish were kept on board the catching boats in small holding tanks that varied in capacity, structure and water flow characteristics. As holding times were much greater than would be expected under a typical catch-and-release scenario this factor was seen as an experimental artefact.

Circle hooks have been promoted widely as ‘fish friendly’ on the expectation that post-release survival rates are higher than for other conventional hook types, due largely to the high frequency of jaw hooking and low incidence of deep hooking. We found significantly lower deep hooking rates for circle hooks (1-4%, depending on species) compared with other conventional hook types (up to 16%). In order to gain acceptance from anglers, however, it is important that circle hooks are at least as effective as conventional hook types. Over two fishing trials we established that circle hooks were at least as effective as conventional hook types for sand flathead. By contrast for dusky flathead, high variability in a small data set obscured any real effect of hook type on catch rate, although results did suggest that the performance of lures probably exceeded that of circle hooks and conventional J-hooks. Further trials with circle hooks would be required to more fully evaluate their relative efficiency for dusky flathead. In practice, the shift from bait to lure fishing for dusky flathead (and to a lesser degree sand flathead) would suggest that the uptake of circle hooks may be low amongst anglers, especially in Queensland and NSW.

Volunteer angler hooking information was available for flathead taken in Tasmania (sand flathead, bait and lure fishing), Victoria (sand flathead – bait fishing, dusky flathead – bait and lure fishing), NSW (dusky flathead – bait and lure fishing) and Queensland (dusky flathead – bait and lure fishing). Fishing with lures resulted in significantly lower deep hooking rates than for bait. Size was also identified as an important factor in deep hooking rates, being lowest in the smallest (effectively sub-legal) size groups.

For both flathead species, regression models revealed significant state effects, either as a main or interaction effect, implying that factors other than method and fish size influenced deep hooking. High deep hooking rates for sand flathead in Victoria (25%) appear to have been related to fishing practice, specifically the use of small hooks to target species other than flathead. Reasons for high deep hooking rates (35%) for bait caught dusky flathead in Queensland were less obvious.

By integrating experimentally determined survival rates with hooking information derived from anglers, the potential impact of catch and release on survival was estimated. Survival rates ranged between 94-99% for most method/state combinations for the two flathead species. Notable exceptions were bait-capture of sand flathead in Victoria and dusky flathead in Queensland. The lower survival rate (91%) associated with the Victorian sample highlights the impact of non-targeted fishing, especially when small hooks are employed. The low survival rate (88%) estimated for bait-caught dusky flathead in Queensland was not considered representative. Consistency between Victorian and NSW survival rate estimates for bait-caught dusky flathead, and those based on the Queensland survival experiment (all about 94%) support this conclusion.

Overall our results indicate that sand and dusky flathead are robust species and that for released fish survival rates are high, supporting the efficacy of current management strategies based on size and bag limits and the practice of catch-and-release fishing. The switch from bait to lures or adoption of circle hooks for flathead are likely to provide benefits for stocks, enhancing the survival of released fish.

Recommendations to maximise survival of released flathead

In developing protocols that can be readily applied to maximize survival in flathead (Objective 3) we developed the “Flathead Survival” information sheet that builds on the results of this project and the “Recfish Code of Practice on Releasing Fish”. The key messages for flathead are:

Survival

Flathead hooked in the jaw have a very good chance of survival if released.

Survival is lower if fish are hooked in the gills or gut and particularly if deep hooking is associated with bleeding.

For gut-hooked fish, cutting the line and not removing the hook improves the likelihood of survival.

Tackle

For bait fishing use hook patterns such as circle hooks to maximise the likelihood that fish are hooked in the jaw.

For conventional hook types, keep line tight to make it less likely that fish will swallow the hook.

The information sheet has been widely distributed and has attracted very positive feedback from anglers.

OUTCOMES ACHIEVED

Key factors influencing post-release survival in sand and dusky flathead have been identified, with hooking location and specifically the incidence of deep hooking (throat or gut) emerging as the most important factor.

Overall, survival rates for sand and dusky flathead have been determined to be high, supporting the efficacy of current management strategies based on size and bag limits and the practice of catch-and-release fishing.

An information pamphlet highlighting protocols that can improve survival potential for flathead has been developed and is being distributed widely to anglers through a range of networks, including Fishcare Volunteer Programs and the National Strategy for Released Fish Survival extension program.

KEYWORDS: Sand flathead, dusky flathead, post-release survival, hooking damage, circle hooks, recreational fishing practices.

PRINCIPAL INVESTIGATOR: Dr J.M. Lyle

ADDRESS: University of Tasmania

Tasmanian Aquaculture and Fisheries Institute

Private Bag 49

Hobart TAS 7001

[slinkymalinky]

That's a great article to post Mariner. Some really good info in there. Particularly interesting to see the scientific back up for the fact that fish can and do expel hooks quickly... I've been challenged on that a few times when justifying fishing to fervent conservationists. Also good to see statistical support for the effectiveness of circle hooks. There are still a lot of fishos who don't believe it.

Thanks, Slinky