|
|
Reducing bycatch without reducing value
Fish Traps with Escape Gaps
Ayana Johnson
INTRODUCTION
Fishing with traps occurs daily on coral reefs all over the world. For the last century, traps have been responsible for a large portion of catch in the Caribbean, and in Curaçao, traps account for more than half of reef fish landings by weight. Trap fishing is notable for its high level of bycatch – traps capture many juvenile and narrow-bodied fishes that are neither desired by fishermen nor desirable as food.
This experiment on the selectivity of fish traps was inspired a fishery ordinance recently proposed by Curaçao’s fishery department. The ordinance includes a requirement that all fish traps have a 20 cm by 2.5 cm gap to allow juveniles and narrow-bodied species to escape. While it is intuitive that such an escape gap would be effective, supporting scientific evidence did not exist. To provide information on the potential ecological and economic implications of a mandated change in trap design, I compared the catch of traditional traps to the catch of traps with escape gaps. 
METHODOLOGY
From May through August 2008, four types of fish traps were tested at three locations on the northwest coast of Curaçao. Standard Antillean arrowhead-shaped traps were tested against traps with one large mesh panel, traps with two 20 cm x 2.5 cm escape gaps, and traps with two 40 cm x 2.5 cm escape gaps (see diagrams at right). At each study location, eight traps (two of each type) were set in 12 to 15 meters of water at marked positions 25 meters apart.
Every week, the traps were placed, closed and then left to soak for three days. The contents of the traps were checked on each soak day (using SCUBA), and the species, length, and condition of each fish was recorded. At the end of every week, the traps were opened and the fish remaining inside were released.
For the purposes of data analysis, fish were categorized in several ways: according to body width (narrow, medium, wide), fish value (low-value, sochi, high-value), and fish family. “Sochi” is a term used to refer to a mixed-species group of reef fish that are often sold collectively at one price. Fish prices were obtained by interviewing fish vendors and asking them to estimate the price at which they purchased various fishes from fishermen. Large mesh traps caught so few fish that those results are not presented here.
RESULTS
Seven weeks of data were collected at each study location, representing 190 trap hauls and 3,336 observations of fish. To avoid double counting, and because traps are generally soaked by fishermen for a single day, only data collected on the first soak day (representing 1,085 fishes) are presented here. Twenty-one species from five families comprise 81.9% of the catch, with Scaridae representing 41.5% of the observations, Haemulidae 13.0%, Chaetodontidae 10.8%, Acanthuridae 10.4%, and Lutjanidae 5.2%. Eels are omitted from the summary data presented below because they are so long and heavy as to dramatically alter the means, although they do not alter the trends.
Key Findings:
• Traps with escape gaps catch about half as many fish as the control traps.
• Escape gaps reduce the catch of narrow-bodied fish (e.g. Chaetodontidae and Acanthuridae) and low-value fish (e.g. Haemulidae) without significantly reducing the catch of high-value fish.
• Fish retained by traps with escape gaps are significantly larger on average than fish in control traps, implying a reduction in the catch of juveniles.
• Large mesh traps caught very few fish overall, supporting fishermen’s resistance to regulating the fishery based on mesh size.
• The catch of all trap types is dominated by parrotfish.
• The market value of the catch is not significantly different between the control, short, and tall gap traps.
DISCUSSION
Reducing Bycatch without Reducing Value
The most important finding of this study is that fishermen could use escape gap traps without decreasing their incomes, because although they would catch fewer low-value fishes and fewer narrow-bodied fishes, the overall mean catch value was not significantly different between trap types. This bycatch reduction is a win-win situation for fishermen and conservation. Fishermen can catch half as many fishes and still make the same amount of money. Fishermen would also reap a longer-term benefit: the juveniles of high-value species that escape via the gaps would be allowed to grow to a more marketable size, and perhaps reproduce, before being caught by a trap with escape gaps.
Potential Benefits of Trap Modification
Switching to traps with escape gaps would have a large effect on coral reef fish populations. Since a trap with large gaps catches a mean of 6.3 fewer fishes than a control trap, retrofitting 10,000 traps (a very low estimate for the number of active traps in the Caribbean) fish traps that each fish 100 days out of the year could reduce bycatch by 6,300,000 fishes. That would have a large impact on coral reef fish populations. Because traps can be easily and cheaply modified to reduce bycatch without reducing catch value, this research has the potential to not only support regulations on the island of Curacao, but also hopefully influence management of trap fishing in many other locations.
Future Research
This is one part of a dissertation designed to examine the ecology and socioeconomics of gear-based options for the sustainable management of coral reef fishing, using Curaçao as a case study. Curaçao is in the formative stages of developing a plan to manage its marine resources, so it is the ideal time for conducting an assessment of the island’s fisheries that can help set the context and framework for management. Also, Curaçao’s reefs are still relatively healthy – there are areas where live coral cover reaches almo st 50%, on par with the healthiest reefs in the Caribbean. This may be the result of relatively low fishing pressure and/or limited use of destructive fishing techniques (gill net use not widespread until recently, dynamite use not recorded). Whatever the cause, the health of Curacao’s reefs provides a rare opportunity in the Caribbean: to design a management strategy that is not merely based on triage.
This material is based upon work supported by the National Science Foundation under Grant No. 0333444.
Any opinions, findings, and conclusions or recommendations expressed in
this material are those of the author(s) and do not necessarily reflect
the views of the National Science Foundation.
Addtional funding from the PADI foundation
Return to top
|
