A voluntary fishing accord

A study: Maximising survival of released undersize west coast reef fish

Below is a summary from this Australian study:

Lenanton, R., St John, J., Wise, B., Keay, I. and Gaughan, D. 2009.
Maximising survival of released undersize west coast reef fish. Final report to Fisheries Research and Development Corporation on ProjectNo. 2000/194.
Fisheries Research Report No. 191. Department of Fisheries, Western Australia. 130p.

Cages were used to investigate the mortality after catch and release angling of snapper Pagrusauratus (Family Sparidae), a recreationally and commercially important demersal species found throughout temperate coastal and shelf waters of Australia. Overall, 65.4% of the 604 snapper caged in the experiment survived release.

Depth of capture was by far the most important factor affecting release mortality. Mortality increased from an average of 3.42% of fish caught in the shallows (5, 15 and 30 m) to 69.0% of fish from the deeper waters (45 and 65m).

Due to the practicalities of catching and caging fish while working at sea it was necessary to mix fish of different sizes in cages and to have different quantities of fish in cages. However, while there was increased mortality associated with increased quantities of fish in cages, this did not affect the result of increased mortality with depth.

Venting, hook pattern, hook location, number of days caged, size of fish (TL in cm) and swimming at release did not affect mortality significantly.

Although mortality in gut-hooked fish was almost three times (91.7%) that of mouth-hooked fish (33.6%), the proportion of gut-hooked fish in the total catch was small (1%of circle hooks and 3% of J hooks).

The clear depth stratification in rates of mortality of snapper indicates that Legal Minimum Length (LML) and or bag limits are suitable management regulations for shallow coastal areas, but that their usefulness decreases at deeper offshore locations. This bodes well for the management of snapper dwelling in the numerous shallow bays, sounds and gulfs around Australia that have well defined boundaries suitable for defining separate management zones.

In contrast, deeper offshore fisheries need to consider management strategies that include alternatives to size and bag limits, and would certainly need to include estimates of post-release mortality when attempting to manage a fishery through controlling total fishing mortality.

Download the full report here