Effect Of Angling And Releasing Eastern Sea Garfish

Researchers for Industry and Investment, New South Wales, Australia are looking into scale loss and mortality in angled and released eastern sea garfish (Hypohamphus australis).

Eighteen species of garfish are angled around Australia, contributing towards a total catch that was most recently estimated at 2.4 million fish during 12 months in 2000/2001. While many of these garfish are consumed or used as bait, approximately 400,000 are released; mainly due to size grading in response to daily bag limits. There are concerns among some anglers that, owing to their fragility, few released garfish survive.

The researchers aimed to investigate this issue for eastern sea garfish during an experiment at Coffs Harbour. Over four days, 185 fish were caught by land-based anglers at the local marina and then released in groups of five into nearby holding cages.

Relevant data were collected on the catching process and the physical condition of fish. Ninety control fish (previously caught at the same location and held in aquaria for up to eight weeks) were similarly caged and all fish were monitored for their survival over 24 hours. At the end of the experiment, five dead and 10 alive angled individuals were assessed for their physical damage using magnetic resonance imaging (MRI).

One control and 93 angled fish died, providing an adjusted mortality rate of 49 per cent for the latter group. The mortalities were mostly attributed to (i) hook ingestion, (ii) scale loss and, to a lesser extent (iii), air exposure. More specifically, only seven fish swallowed their hooks, but all died. For the remaining mouth-hooked fish, those that lost more than approximately 40 per cent of their scales, or were exposed to air for greater than 21 seconds had much greater chances of dying.

Neither hook ingestion nor air exposure were attributed to any particular fishing or handling method. However, greater scale loss clearly occurred when fish were held with dry bare hands, dropped on the ground and exposed to air or confined in 20-l buckets for long periods prior to being released. For most fish, physical damage was limited to scale loss, since MRI revealed few compression injuries. Similarly, there were no significant differences in deeper dermal trauma among MRI-assessed fish, although on average, the fatalities had more abrasions than the survivors. Fish that were not touched at all lost very few scales and most (94 per cent) survived.

The results indicate that angled-and-released eastern sea garfish can incur high mortality, but that this can be dramatically reduced if fish are quickly released without any physical contact. Such a protocol could also alleviate negative impacts among other angled-and-released fish, especially those that are prone to scale loss or skin damage.

July 2010

the Fish Site Editor

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