The structure of a nearshore fish assemblage at an oceanic island: insight from small scale fisheries through bottom traps at Gran Canary Island (Canary Islands, eastern Atlantic)

Abstract

-Unsuitable management of fisheries may lead to overexploitation of marine resources. Oceanic islands with narrow continental shelves, in particular, are sensitive to unsustainable levels of fishing intensity. Fish traps are the modality of artisanal professional fishing more important in the coastal waters of the Canary Islands (eastern Atlantic) to capture demersal resources, which are deployed all year-round and allow a release of undersized captures. We aimed at studying the structure of nearshore fish assemblages through deployment of benthic bottom traps carried out at Gran Canary Island. A quantitative description of catches, in terms of abundance, biomass and sizes, of traps deployed from May to October 2009, between ca. 20 to 50 m depth, was carried out. We used this information to test whether the structure of nearshore fish assemblages at the island scale varied between three zones located at the NW, NE and E of the island with varying habitat structure. A total of 58 species (22 families) were collected for the overall study from a total of 2568 deployed traps. The species Sparisoma cretense (25% of the total biomass), the family Sparidae (16 species, 44%) and Mullus surmuletus (4%) accounted for more than 73% of the total catch in terms of biomass. The parrotfish, S. cretense, was the fish with the largest catches in terms of number of individuals, followed by Dentex gibbosus, Diplodus vulgaris, Stephanolepis hispidus, Chromis limbata and Mullus surmuletus. Differences in the structure of the fish assemblage at the island scale were not predicted by differences in the type of bottom. Fishing yields were similar between the NW (0.16 ± 0.02 kg trap −1 day −1 ) and NE side of the island (0.19 ± 0.01 kg trap −1 day −1 ), being lower at the E zone (0.15 ± 0.01 kg trap −1 day −1 ). The most abundant species, the parrotfish S. cretense, had a mean size close to its first maturity sizes (SFM 50 ), while both D. gibbosus and D. vulgaris were below SFM 50 . In general, the mean size of Sparids was well below SFM 50 , an indication of overexploitation, while M. surmuletus and S. hispidus reached a mean size beyond their first maturity sizes.

Geographical Range Extension of the Spotfin burrfish, Chilomycterus reticulatus (L. 1758), in the Canary Islands: A Response to Ocean Warming?

“…The increase in numbers of C. reticulatus in Gran Canaria island cannot be related to relaxed fishing efforts, because nearshore local stocks are still heavily exploited, mainly by traps [66], nor to specific conservation strategies, since there is not a specific conservation strategy for this reef fish. At present, the population structure of C. reticulatus at both islands seems quite similar, mostly including medium and large-sized individuals, with isolated sightings across the entire nearshore perimeter.…”

Anthropogenic disturbances and conservation of coastal environments in an oceanic archipelago

“…Falcón et al, 1996;Tuya et al, 2004) and currently, this situation is worsening because of the growing importance of shore recreational fishing, and other activities such as uncontrolled shellfishing or indiscriminate harvesting, as well as to a lesser extent illegal underwater fishing Hernández-García 2012, Corral et al, 2017). Canarian fishery catcheries have experienced a sharp decrease in the last four decades, from 2.2 kg trap -1 day -1 in the 1970's to 0.15-0.19 kg trap -1 day -1 (Castro and Hernández-García 2012;García-Mederos et al, 2015). The development of an efficient management plan is a daunting task (e.g.…”

“…oversizing of professional fleet and recreational fishing through the last decades (Zeller et al, 2008;Sistiaga 2011). Other "biological" factors contribute to this situation, such as the high variety of commercial fish, approximately 100 species, and the necessity to update the minimum size of captures (García-Mederos et al, 2015).…”

“…Catcheries have shown clear symptoms of overfishing throughout the last decades (García-Mederos et al, 2015). The steadily increasing pressure from recreational fishermen is a factor of utmost importance to take into account for future works on fisheries effort and landings.…”

“…Professional fishers are currently limited to certain coastal settlements, focused on a very limited array of target species (Balguerías 2001), and represent a minor fraction of the landings. The collapse of several commercial species is eminent in the near future since the fishing pressure is not decreasing and stocks are on the brick of sustainability for most of the species, with special emphasis on groupers and snappers (García-Mederos et al, 2015). Riera et al, (2016) have shown a dramatic decrease of two commercial limpet sizes (Patella candei crenata and Patella aspera), indicative of overharvesting, mainly conducted by recreational harvesters.…”