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.

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.

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.

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.

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.

Comparing Atlantic and Mediterranean populations of the velvet belly lanternshark, Etmopterus spinax, with comments on the efficiency of density-dependent compensatory mechanisms

Etmopterus spinax is a small-sized deep-water lantern shark that occurs in the Eastern Atlantic and the Mediterranean. Differences in depth distribution, densities, size at maturity and fecundity were compared between a population that has suffered high levels of fishing mortality during the last decades (Southern Portugal in the northeast Atlantic) and a population where low fishing pressure below 500 m occurs at present or has occurred in the last decades (Northern Alboran Sea in the western Mediterranean). The density of this species, as derived by experimental bottom trawl survey, off the coast of Southern Portugal, is substantially lower than in the Northern Alboran Sea throughout the entire depth range. The Atlantic population is maturing at smaller sizes than the Mediterranean population and has a lower mean fecundity. Specifically, sizes at maturity for Southern Portugal and the Northern Alboran Sea were, respectively, 25.39 and 28.31 cm TL for males and 30.86 and 34.18 cm TL for females, while mean fecundities for Southern Portugal and the Northern Alboran Sea were, respectively, 9.94 and 11.06 oocytes per mature female. This work demonstrated the possible presence of density-dependent mechanisms in the Southern Portuguese population of E. spinax that has lowered the size at maturity as a possible result of excessive fishing mortality. However, given that this is an aplacentary viviparous shark, where fecundity is dependent on female size, this compensatory mechanism seems to have a limited efficiency.

Depth distribution of the velvet belly, Etmopterus spinax, in relation to growth and reproductive cycle: The case study of a deep-water lantern shark with a wide-ranging critical habitat

The velvet belly lantern shark, Etmopterus spinax (Squaliformes: Etmopteridae), is a small-sized squalid shark commonly found in deep waters off the Portuguese coast, mainly on soft bottoms. In this study, 67 research cruise bottom trawl tows (with 1-hour duration) were carried out at depths that ranged from 84 to 786 m. A total of 396 specimens (192 males and 204 females) were caught, with total lengths and ages ranging, respectively, from 10.2 to 32.9 cm and 0 to 7 years for males and from 9.8 to 41.1 cm and 0 to 10 years for females. Size, age, sex and maturity stages were found to be correlated with depth, with the larger, older and mostly mature specimens occurring predominantly at greater depths. There seems to be a depth-related migration, where the pregnant females migrate from deeper mating grounds to shallower nursery grounds. The sex ratios were relatively similar in the shallower strata, but females dominated at more than 600 m and were exclusive at more than 700 m. Fishing-related mortality may have complex and significant repercussions on this species, given that commercial fisheries are impacting different segments of this population differently.

Feeding habits of the velvet belly lanternshark Etmopterus spinax (Chondrichthyes : Etmopteridae) off the Algarve, southern Portugal

Etmopterus spinax is one of the most abundant predators of the upper continental slope off the Algarve (southern Portugal), where it is captured in large quantities in deep-water fisheries. The feeding habits of E. spinax off the Algarve were investigated through the analysis of stomach contents of 376 individuals. Prey composition was described and maturity, sex and size related variations in the diet analysed. The overall diet of E. spinax suggested a fairly generalized benthopelagic foraging behaviour primarily tuned to pelagic macroplankton/microneckton, teleost fish and cephalopods. Sex and maturity related differences in the diet were not significant. Two main ontogenic diet shifts were observed at about 17 and 28 cm total length. Small and medium sized immature sharks had a diet dominated by eurybathic crustaceans, chiefly Meganyctiphanes norvegica and Pasiphaea sivado. Larger individuals consumed more teleosts and cephalopods, in part associated with scavenging as a new feeding strategy. With increasing shark size the diet diversified both in terms of resources exploited and prey size.

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.

Life history of a wide-ranging deepwater lantern shark in the north-east Atlantic, Etmopterus spinax (Chondrichthyes: Etmopteridae), with implications for conservation

In this paper, the population biology of the velvet belly lanternshark Etmopterus spinax was studied and life-history coefficients determined. Age was estimated from sections of the second dorsal spine and validated by marginal increment analysis. Males attained a maximum age of 8 years while 11 year-old females were found. Several growth models were fitted and compared for both size-at-age and mass-at-age data, showing that even though this is a small-sized species, it has a relatively slow growth rate. This species matures late, specifically at 49.6 and 42.5% of the maximum observed ages for males and females, respectively. It has a low fecundity, with a mean ovarian fecundity of 9.94 oocytes and a mean uterine fecundity of 7.59 embryos per reproductive cycle. This species seems to have a long reproductive cycle, and even though no conclusive data were obtained, a 2-3 year cycle is possible. The estimated coefficients indicate that this species has a vulnerable life cycle, typical of deepwater squalid sharks. Given the high fishing pressures that it is suffering in the north-east Atlantic, this fish may already be facing severe declines or in risk of facing them in the near future. (C) 2008 The Authors Journal compilation (C) 2008 The Fisheries Society of the British Isles

Demography of a deep-sea lantern shark (Etmopterus spinax) caught in trawl fisheries of the northeastern Atlantic: Application of Leslie matrices with incorporated uncertainties

The deep-sea lantern shark Etmopterus spinax occurs in the northeast Atlantic on or near the bottoms of the outer continental shelves and slopes, and is regularly captured as bycatch in deep-water commercial fisheries. Given the lack of knowledge on the impacts of fisheries on this species, a demographic analysis using age-based Leslie matrices was carried out. Given the uncertainties in the mortality estimates and in the available life history parameters, several different scenarios, some incorporating stochasticity in the life history parameters (using Monte Carlo simulation), were analyzed. If only natural mortality were considered, even after introducing uncertainties in all parameters, the estimated population growth rate (A) suggested an increasing population. However, if fishing mortality from trawl fisheries is considered, the estimates of A either indicated increasing or declining populations. In these latter cases, the uncertainties in the species reproductive cycle seemed to be particularly relevant, as a 2-year reproductive cycle indicated a stable population, while a longer (3-year cycle) indicated a declining population. The estimated matrix elasticities were in general higher for the survivorship parameters of the younger age classes and tended to decrease for the older ages. This highlights the susceptibility of this deep-sea squaloid to increasing fishing mortality, emphasizing that even though this is a small-sized species, it shows population dynamics patterns more typical of the larger-sized and in general more vulnerable species. (C) 2014 Elsevier Ltd. All rights reserved.