Methods contributing to fishing selectivity around FADs

Good mastering of fishing selectivity is needed to:

  • Reduce the catches of juveniles
  • Target some species in order to reduce the catches of an overexploited species
  • Improve the economic performance of the companies and the sailors’ working conditions
  • Diversify fishing activities and allow the stabilization of the landings consisting of migratory species happening during the year (maintenance of the activity during the year, better management of the storage and commercialization tools of the products.)

Several factors may influence the nature (specific composition and size) and importance of the catches around FADs:

A) The mode of exploitation of FADs and the targeted species

A comparison between three islands close to one another (Guadeloupe, Dominica and Martinique) evidenced a sensible difference in the specific composition of the landings.

Country

Date

Blue marlin (%)

Yellow fin tuna (%)

Sea bream (%)

Guadeloupe

2008 and 2010

18 and 9

36 and 35

33 and 29

Dominique

2010

7

32

16

Martinique

2009 and 2010

44 and 36

15 and 25

9 and 4

Proportion of main species in the FAD catches of 3 close islands (Mathieu et al. 2013)

Catches per species around moored FADs of Guadeloupe, Dominica and Martinique

This difference in the specific composition partly depends on the mode of exploitation of the FAD (Guyader et al. 2013). When fisherfolk target the dolphin fish (case of Guadeloupe), they exploit several FADs per trip because this species lives in small schools scattered under floating objects. Fishing yellow fin tuna or marlins, on the contrary calls for a reduction of the number of FADS so that the concentration of fish always occurs on the same device. Fish’s preferred paths are not well known, so as how they evolve from a year to the following. The geographic position of the islands probably influences the fishing results.

B) FAD spacing regarding the coast

According to the observations made in Martinique, the spacing of the FADs influences the landings per trip, per fishing hour and per device. The catches increase as fisherfolk get away from the coast. It is mainly the catches of yellow fin tuna and a little less skipjack tuna that evolve the most according to the distance. Marlins seem to have a lower yield within the 12 nautical miles. It could be due to the fact that the captains of small vessels, more numerous near the coast, would rather avoid this species for safety reasons.

C) Fishing season

According to the times of the year, the fishing yields and specific composition of the landings vary a lot. The example of Martinique shows that in 2004 and 2005, good yields were obtained in March-April with blue marlins and September-November with yellow fin tuna. During the intermediate period, the yields per trip were lower. Given that the best black fin tuna season was the month of July and knowing that this species is abundant at the adult stage (“intermediate layer tuna”) – see description of the aggregations around FADs), it could be interesting to search for appropriate techniques in order to valorize better those concentrations of fish.

Seasonality of the catches around anchored FADs (Martinique 2004 and 2005)

One must nonetheless keep in mind that the fishing seasonality is not the same all over the Caribbean. As fish move, the landing peeks differ from one country to another. An example is given with blue marlins mainly present in Martinique at the beginning and end of the year while it only shows an annual peek of catch by effort unit in Bermuda in July. These data suggest that this species migrates towards the North to reach Bermuda in the middle of the year and comes back South during the second part of the year.

Comparison of the average blue marlin catches per trip in Martinique and Bermuda. (blue – observed; pink – mobile averages) (Excerpt of SCRS/2005/2010)

D) Fishing gears and techniques

The specific composition and size of the catches was studied based on 54 fishing trips in Martinique on professional fisherfolk’s skiffs between August 2003 and April 2004 (Reynal et al. 2007).

The study of catches around the FADs shows that a relatively important quantity of small tuna (length at the fork <40 cm) is captured (422 individuals over 54 professional fishing trips). They are caught at daytime with surface trolling lines (143 individuals) but mostly with deep trolling lines (250 individuals).

Intermediate sized tuna (between 40 cm and 1 m) are captured at nighttime as well as at daytime. At daytime they are fished at greater depths than smaller ones (84% with deep trolling lines and 16% with surface trolling lines). At nighttime, black fin tuna seem to behave differently regarding trolling lines. Right before sunrise, fisherfolk catch them with lines going as deep as 30 m. This type of fishing is not used during the day (from 6 AM roughly). Other tuna fish (yellow fin tuna, skipjack tuna etc.) are less frequently fished with that particular technique.

Except dolphin fish, wreck fish are rarely targeted by professionals and are consequently less featured in their catches. Dolphin fish are captured with trolling lines or baited lines called “hunters”. (Guillou and Lagin 1997). This fishing technique is particular to dolphin fish fishing. It consists in maintaining the first captured fish along the edge. Very gregarious, sea breams live in schools lead by a dominant male. These schools are relatively small when compared to tunas’ and tend to set near drifting wrecks. That is the reason why fisherfolk who wants to target that particular species multiply the number of FADs, as it is done in Guadeloupe.

Large size fish (billfish, yellow fin tuna of more than a meter long) are very sought for at daytime. They are practically always fished with drifting vertical longlines. Yellowfin tuna of more than a meter were caught at greater depths (below 80 m) than tuna of intermediate size. Such observations suggest that tuna distribute according to their size, from the surface where the smallest individuals tend to be as deep as 180 m (maximum depth at which the largest individuals were caught). However, some fisherfolk report catches of large yellow fin tuna at nighttime with trolling lines ill-adapted for catching these fish. Contrary to tuna, no spearfish (except swordfish) appear to have been caught at nighttime.

In 2013, the experimentation of new devices in the framework of the MAGDELESA project was tested: jigging, which is a vertical fishing technique exploiting the entire water column over the first 100 meters, and popper which is a floating lure used on traditional trolling lines. During experimental fishing activities, the main captures made with a jig around FADs were mostly black fin tuna (68,7%), then yellow fin tuna (14,6%) and skipjack tuna (11,4%). If more than 80% of the black fin tuna captured with a jig were mature, all of the yellow fin tuna captured were juveniles. Jigging appears to be an efficient technique to target and capture adult black fin tuna. Yellow fin tuna as well as spearfish can exceptionally be captured with the jigging technique. With a popper, the captures mainly consisted in black fin tuna (56,8%) and yellow fin tuna (38,1%). As this device operates at the surface in the aggregation layer of juvenile tuna (Doray, 2006), 81,9% of the captures were of not mature individuals. Captures of adult yellow fin tuna made with a popper were nonetheless observed.

Model of Williamson Benthos jig

Model of Daïwa Saltiga popper

E) The baits used on drifting vertical longlines

Seven to fifteen drifting vertical longlines with one hook constitute a skiff’s fishing arsenal. These devices are generally baited with small live tuna captured with trolling lines. Different species were tested as baits. Black fin tuna has better yields while longlines baited with skipjack tuna and yellow fin tuna have respective capture yields of 11 and 7%. Trials were also performed with coubali carangs (n=3) and flying fish but in a too small quantity to enable the establishment of a final conclusion. These trials enabled 100% of capture, which should encourage the performance of future experimental fishing trips to test these new baits.

Live baits

Baits

Number of longlines set

Number of catches

% of capture

Yellow fin tuna

41

3

7%

Listao tuna

168

18

11%

(multicolored)

 

 

 

Coubal carangs

3

3

100%

Flying fish

1

1

100%

Efficiency of live baits on drifting vertical longlines around anchored FADs

 

When there are not enough live baits, the fisherman can use dead baits. He thus cut pieces of tuna (called “bouchon” or “dolle”) coming from the catches of the day before or of that very day, or uses fresh flying fish. Different baits were tested as well as frozen squid (experimental bait). The best yields were obtained on vertical longlines baited with “bouchon” (27%) and fresh flying fish (22,5%). Frozen squid does not seem to be an efficient bait (6% of capture and 11.5% when coupled with a “bouchon”). The use of flying fish (fresh or frozen) seems to be a potential solution to substitute the use of tuna juveniles as baits. This would sensibly reduce the consumption of fuel (reduction of trolling time) and would let fisherfolk use other techniques such as jigging.

It is worth noting that marlins are exceptionally captured with dead baits or flying fish. 

Dead baits

Baits

Number of longlines set

Number of catches

% of capture

Frozen squid

110

7

6%

Bouchon* + squid

26

3

11,5%

Flying fish

71

16

22,5%

Bouchon*

177

48

27%

Flying fish + Bouchon*

1

1

100%

                                                              *Bouchon = piece of tuna used as a bait

Efficiency of dead baits on drifting vertical longlines around anchored FADs

F) Elements for discussion on improving anchored FAD fishing

Even if the capture of tuna juveniles remains rather low around FADs (a dozen individuals per trip), the experimentation of new baits should continue in order to avoid that fisherfolk spend time and fuel to catch these live baits. The experimentation of frozen flying fish as a bait through an adequate method to avoid its blackening or the use of small live coastal pelagic fish should be tried. Further experimentations of techniques such as jigging, fire fishing at nighttime etc. need to be conducted while making sure not to damage fisherfolk’s working conditions. So as to prevent excess development of fishing activities on certain resources, an effort must also be made to assess the populations of targeted species, in particular black fin tuna and dolphin fish, and to improve knowledge of the resources such as marlins. If setting the FADs further from the coast seems to increase the number of catches, fishermen must use adequate gears to go offshore and costs should not be higher than benefits. The governance of FAD parks should also take into account FAD accessibility by fisherfolk all year long and according to the capacity of their fishing units.