Biology, population dynamics, management and conservation of deep water lantern sharks, Etmopterus spinax and Etmopterus pusillus (Chondrichthyes: Etmopteridae) in southern Portugal (northeast Atlantic)

Tese dout., Ciências e Tecnologias das Pescas, Universidade do Algarve, 2007

Biologia alimentar do Etmopterus pusillus no Algarve

Dissertação mest., Biologia Marinha, Universidade do Algarve, 2007

Length at first maturity of two species of lantern sharks (Etmopterus spinax and Etmopterus pusillus) off southern Portugal

Etmoplerus spinax and Etmopterus pusillus are captured in large quantities in some deep-water fisheries along the Portuguesc coast and are always discarded. Specimens were collected from February 2003 to May 2004 from deep-water fisheries and classified as mature or immature. Maturity ogives were fitted and size at first maturity estimated for each sex of each of each species. Both species are late maturing, with the maturity size varying between 75% and 87% of the maximum observed sizes, depending on species and sex. For both species, females tended to mature at and grow to larger sizes than males. The late maturation of these deep-water shark species make these populations extremely vulnerable to increasing fishing mortality.

Population parameters of the smooth lantern shark, Etmopterus pusillus, in southern Portugal (NE Atlantic)

Etmopterus pusillus is a deep water lantern shark with a widespread global distribution that is caught in large quantities in some areas, but is usually discarded due to the low commercial value. In this work, the population biology was studied and life history parameters determined for the first time in this species. Age was estimated from sections of the second dorsal spine and validated by marginal increment analysis. Males attained a maximum age of 13 years, while 17-year-old females were found. Several growth models were fitted and compared for both size and weight at age data, showing that even though this is a small sized species, it has a relatively slow growth rate. This species matures late and at a relatively large size: at 86.81% and 79.40% of the maximum observed sizes and at 58.02% and 54.40% of the maximum observed ages for males and females, respectively. It has a low fecundity, with a mean ovarian fecundity of 10.44 oocytes per reproductive cycle. The estimated parameters indicate that this species has a vulnerable life cycle, typical of deep water squalid sharks. Given the high fishing pressures that it is suffering in the NE Atlantic, the smooth lantern shark may be in danger of severe declines in the near future. (c) 2007 Elsevier B.V. All rights reserved.

Feeding ecology of the deep-sea lanternshark Etmopterus pusillus (Elasmobranchii: Etmopteridae) in the northeast Atlantic

This study provides the first description of the feeding ecology of the smooth lanternshark Etmopterus pusillus based on stomach contents of specimens caught as bycatch in the Algarve (southern Portugal) with bottom trawling and bottom longline. The diet of E. pusillus consists mainly of fish (dry weight (% W)=87.1%; frequency of occurrence (%FO)=28.6%; number (%N)=30.3%), crustaceans (%W=7.7%; %FO=36.7%; %N=3.4%) and cephalopods (%W=4.7%; %FO=11.3%; %N=11.1%). The diet did not vary between sexes. Ontogenic changes were detected: crustaceans decreased in importance as the sharks increased in size and fish became dominant in the diet of adults. Combining two fishing methods provided broad information on the diet of E. pusillus, as bottom trawling caught smaller specimens and longlines caught larger individuals. E. pusillus feeds mainly on non-commercial species, and therefore does not compete directly with commercial fisheries. Finally, E. pusillus feeds in various parts of the water column and thus it can access a wide range of prey; however, this also means that it can be caught by both gears, making it more vulnerable in terms of conservation.

Effects of fishing methods on deep water shark species caught as by-catch off southern Portugal

Deep water sharks are commonly caught as by-catch of longlines targeting bony fishes and trawlers targeting crustaceans in deep water off the southern Portuguese coast. Due to low or no commercial value, these species are most of the times discarded at sea, with only the larger specimens of some species commercialized at very low prices. In this study we present size distributions, maturity distributions, and sex ratios of 2,138 specimens belonging to four different species, namely the lantern sharks Etmopterus pusillus and Etmopterus spinax and the catsharks Galeus melastomus and Galeus atlanticus, caught with these two gears. Trawls generally caught smaller-sized specimens, in a wider length range than longlines. Trawls caught mostly immature specimens of all species, namely 83.7% immature of E. pusillus, 84.3% of E. spinax, 89.5% of G. melastomus, and 95.5% of G. atlanticus, while longlines caught mostly immature E. pusillus (69.2%) and G. melastomus (78.6%) and mostly mature E. spinax (88.2%) and G. atlanticus (87.2%). Trawls tended to catch more males than females of all species except E. spinax, while longlines caught more females than males of E. spinax and G. melastomus and more males than females of the other two species. The main conclusion of this work is that trawls are catching smaller-sized and mostly immature specimens when compared to longlines, meaning that they are probably having a more detrimental effect on these shark populations. The data presented here have significant implications for the conservation of these shark populations since sizes, sexes, and the immature and mature components of the populations are being affected differently by these two fishing gears.

Identification of deep water lantern sharks (Chondrichthyes : Etmopteridae) using morphometric data and multivariate analysis

Taxonomic distinction to species level of deep water sharks is complex and often impossible to achieve during fisheries-related studies. The species of the genus Etmopterus are particularly difficult to identify, so they often appear without species assignation as Etmopetrus sp. or spp. in studies, even those focusing on elasmobranchs. During this work, the morphometric traits of two species of Etmopterus, E. spinax and E. pusillus were studied using 27 different morphological measurements, relatively easy to obtain even in the field. These measurements were processed with multivariate analysis in order to find out the most important ones likely to separate the two species. Sexual dimorphism was also assessed using the same techniques, and it was found that it does not occur in these species. The two Etmopterus species presented in this study share the same habitats in the overlapping ranges of distribution and are caught together on the outer shelves and slopes of the north-eastern Atlantic.

The hake deepwater semi-pelagic ("pedra-bola") longline fishery in the Algarve (southern Portugal)

A 2-year study of the European hake (Merluccius merluccius) semi-pelagic ("pedra-bola) longline fishery was carried out in the Algarve (southern Portugal). This fishery takes place on the continental slope at 200-700 m depths. using monofilament longlines that are lifted off the bottom at regular intervals by glass balls. Hook selectivity trials were carried out with four hook sizes (SIAPAL brand numbers 10, 9, 7 and 5) from March to August 1997 and May to August 1998. At least 32 species of fish and invertebrates were caught, with hake dominating the catch (41 and 45% of the catch in numbers), followed by Galeus melastomus (23 and 19%), Micromesistius poutassou (10 and 7%), Benthodesmus elongatus (8 and 5%), Etmopterus pusillus (6 and 9%) and Scyliorhinus canicula (5 and 4%). Apart from the hake, and some species of commercial value such as G. melastomus (only the large individuals), Ray's bream (Brama brama, 1.4 and 4%), silver scabbard fish (Lepidopus caudatus. 1 and 2.5%), swordfish (Xiphins gladius, <1%), wreckfish (Polyprion americanus, <1%). conger eel (Conger conger. <1%), and bluemouth rockfish (Helicolenus dactylopterus, <1%)- most of the other species are discarded, used as bait in traps or consumed by the fishermen. Catch rates (number of fish per 100 hooks) for hake and for all species combined decreased significantly with hook size. Hake catch size frequency distributions for the different hook sizes in 1997 and 1998 were highly overlapped, with the four different hooks catching a wide range of sizes. Although catch size frequency distributions for the different sized hooks were not significantly different in 1997, hake caught in 1998 were characterised by smaller sizes and size ranges. (C) 2001 Elsevier Science B.V. All rights reserved.

Size at maturity and length-weight relationships of the blurred lantern shark Etmopterus bigelowi (Squaliformes: Etmopteridae) caught off southeastern Brazil

The blurred lantern shark Etmopterus bigelowi, a deep-water squaloid shark, is globally widespread in temperate and tropical waters, but there is little available information about its biology owing to its relative rarity of capture and taxonomic confusion with its sibling species Etmopterus pusillus. Specimens used in this study were collected from July to December 2004 as by-catch in the commercial deepwater trawl fishery targeting red shrimp Aristaeomorpha foliacea in the southwestern Atlantic. We examined 55 specimens (22 males and 33 females) ranging in total length (TL) from 31.5 to 73 cm and in total weight from 103 to 1600 g. Length-weight relationships were explored for each sex and significant differences were found in the slope coefficients of the male and female regressions. The size at maturity for each sex was evaluated fitting a logistic regression. Females matured at larger sizes than males, with estimated sizes at first maturity of 56.0 cm TL for females and 45.1 cm TL for males. The present study provides important preliminary information about E. bigelowi that can be incorporated in risk assessment and stock assessment models, essential for efficient management practices aimed at avoiding overexploitation of these vulnerable deep-sea sharks.

Semi-pelagic Longline and Trammel Net Elasmobranch Catches in Southern Portugal: Catch Composition, Catch Rates and Discards

In Portugal, elasmobranch landings have decreased substantially in recent years. In this work, elasmobranch catches in semi-pelagic longlines (1997 and 1998) were compared with those in trammel nets (2000) in the Algarve, southern Portugal areas. In the semi-pelagic longline fi shery, 7 elasmobranch species represented 33.4% (2 185 specimens) of the total fi sh catches. Among the elasmobranch species, the most abundant were Galeus melastomus (63.3%), Etmopterus pusillus (21.7%) and Scyliorhinus canicula (14.2%). Most of these elasmobranchs were discarded (68.3% in total). In the trammel net fi shery, 16 different elasmobranch species represented 4.3% (597 specimens) of total fi sh catches and the most important species were Raja undulata (43.6%) and S. canicula (10.2%). The majority of the elasmobranchs caught in trammel nets had commercial value, and only 5.4% were discarded. In both fi sheries, intra-specifi c catch rates varied with depth. Length-frequency distributions for the only species with relatively high catches in both fi sheries, S. canicula, showed that, in general, trammel nets catch larger specimens and in a narrower length range than do longlines.