The effects of trap fisheries on the populations of Caribbean spiny lobster and reef fish species at the Saba Bank
The Caribbean spiny lobster (Panulirus argus) is a widespread crustacean species. It inhabits shallow water reefs and rocky substrates from Brazil to Florida. The lobster fishery is one of the most important fisheries in the Caribbean (in 2011 the total catch was 35,642 tons), generating more than 456 million US dollars annually. However, the annual landings of P. argus throughout the Caribbean have been in decline since 1995 (FAO, 2013). Over-exploitation is thought to be one of the major causes of this decline (CRFM, 2011).
One of the areas where the spiny lobster fishery is important, is on the Saba Bank, a 2,200 km2 submerged plateau, near Saba in the northern Caribbean Sea. Spiny lobsters are fished exclusively with traps by nine small (11m) vessels operating from Saba. To determine the current status of the P.argus stock and its fishery on the Saba Bank, basic fisheries data were collected in 2012 and compared with similar studies conducted in 1999 and 2007.
The number of lobster traps hauled per fishing trip increased from 59 to 80 between 1999 and 2012 while the number of lobsters landed per trip decreased from 83 to 52 per trip during the same period. A similar declined was observed in the standardized (75 trap hauls per trip) CPUE both in number and total weight of lobster landed. No obvious changes in fishing areas on the Saba Bank were observed during this period.
The total catch of lobster was estimated as 62 t, 92 t and 38 t in 1999, 2007 and 2012, respectively. The high catch in 2007 was attributed to the higher number of estimated fishing trips in 2007 (1000) compared to 1999 (650) and 2012 (600). The lower estimated annual catch in 2012 compared to 1999 is attributed to a decline in CPUE. These result suggest a decrease in abundance of spiny lobster on the Saba Bank between 1999 and 2012, similar to decline observed in the wider Caribbean.
Size-at-maturity (CL50%) for male P.argus was found to be 92.2 (± 2.53 SE) mm carapace length, slightly below the minimum legal size (95mm CL). The mean size of landed male (109 mm CL) and female lobster (105 mm CL) showed that predominantly large, mature lobster are landed. Berried female spiny lobsters were observed on the Saba Bank throughout the year with a peak from March to June.
In addition to lobster, mixed reef fish were also landed in the lobster trap fishery. A total of 57 fish species were identified in the catches. Roughly 15 kg of mixed reef fish was landed per lobster trip, resulting in an estimated 8-10 t of mixed reef fish landed in 2012. The species composition (in weight) of the landed mixed fish consisted mainly of grunts (Haemulon album, H. melanurum and H. plumierii 30%), small groupers (Epinephelus guttatus and Cephalopholis fulva 17%) and queen trigger fish (Balistes vetula 21%). Only the mean total length of landed E. guttatus decreased significantly between 1999 (33 cm TL) and 2012 (31 cm TL).
In addition to the landed mixed fish, an estimated 10 t of mixed fish was discarded in 2012. The species composition (in weight) of the discarded mixed fish consisted mainly of grunts (H. melanurum and H. plumierii 34%), boxfishes (Acanthostracion quadricornis and A. polugonia 19%) and nurse sharks (Ginglymostoma cirratum 9%).