Elasmobranchs around the Maltese Islands : field and fisheries study for conservation

Abstract

Elasmobranchs have long been exploited by the Maltese fisheries sector, however to date no scientific study has been conducted evaluating the effect that such practices are having on the stocks of these species. Therefore, this study aimed at bridging this gap in information, in order to provide detailed scientific data for the management of this highly vulnerable subclass. In addition to this, it was also important to survey the Maltese coastal waters to provide information on the species present in this area along with information on the habitats utilized by these species. Hence, for the purpose of this study, the elasmobranch fisheries landings data over the period between 1952 and 2003 were considered, market surveys were conducted at the fish market and coastal field surveys involving SCUBA diving techniques were carried out around the Maltese islands. The results obtained during this study outline a significant decline in the landings reported over the 1952 to 2003 period, which is in sharp contrast to the increase in fishing effort occurring over the same period. This decrease may be linked to a number of factors, one of which being over-exploitation, as is probably the case for Prionace glauca whose landings between 1985 and 1987 fell by over 75%. Exacerbating this problem is the exploitation of elasmobranchs during their most sensitive life history stages (Cortes, 2002; Frisk et al., 2002). In fact, for species such as Hexanchus griseus, Prionace glauca and Squalus blainvillei, a significant part of the entire sample set recorded at the fish market, was composed of immature individuals. Amongst the species landed locally and recorded during this study it was also observed that the most important shark species, in terms of abundance was Scyliorhinus canicula, whilst the most important batiod species in terms of abundance was Dipturus oxyrinchus. The months January to June are observed to be the most important in terms of elasmobranch landings, a trend which was also observed to be statistically significant. This is mainly because the majority of the species landed locally are caught using bottom longlining techniques, which are widely practiced by the Maltese fishermen during these months. During the coastal field surveys, only one shark species was recorded, this being Squatina squatina, whilst seven batoids species were observed amongst which the most frequently encountered species was Dasyatis pastinaca. A species, which on a number of survey dives conducted during the month of July 2002 at Ghajn Tuffieha, was also recorded in a significantly larger abundance over a short time frame. Measures such as the improvement of the fishing techniques in order to reduce the by-catch and the exploitation of the sensitive life history stages of these species, need to be considered in order to reverse the observed declining trends. Other actions such as the enactment of laws protecting species whose stocks are known to be badly depleted or which are known to be very sensitive to exploitation should be considered. Conservation management measures for the protection of those species occurring in the coastal waters should also be taken into consideration when planning Marine Conservation Areas.