Comparing Zostera and Spartina environments in relation to carbon burial: a sedimentary and geochemical approach from Ria Formosa

Dissertação de mestrado, Biologia Marinha, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2015

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.

A conservation trade-off? Interspecific differences in seahorse responses to experimental changes in fishing effort

1. A 2-year experimental seining programme and underwater visual censuses were undertaken to quantify the direct effects of active demersal fishing on the population structure and relative abundance of two sympatric seahorse species of conservation concern: the European long-snouted seahorse, Hippocampus guttulatus Cuvier 1829 and the short-snouted seahorse, Hippocampus hippocampus L. The influence of habitat preference on population-level responses to changes in habitat structure following a reduction in fishing effort was also investigated. 2. It was predicted that the benthic habitat would be more structurally complex after fishing ceased and that seahorse densities would increase in response to reduced fishing mortality. Furthermore, it was predicted that the magnitude of the increase in density would be greater for H. guttulatus than for H. hippocampus, because the former species prefers complex vegetated habitats while the latter species uses sparsely vegetated habitats. 3. As predicted, the amount of habitat cover increased significantly when seining ceased, primarily through increases in the abundance of drifting macroalgae and unattached invertebrates. Despite similarities in life histories, the two seahorse species responded differently in terms of magnitude and direction to reduced fishing effort: the abundance of H. guttulatus increased significantly while H. hippocampus decreased in abundance. 4. Results suggest that active demersal fishing may influence the magnitude and direction of the responses of benthic marine fishes to exploitation through its impacts on habitat structure. An increase in habitat cover appeared to favour higher densities of H. guttulatus when seining effort was reduced. By contrast, repeated seining, which maintained less complex habitats, appeared to favour greater abundances of H. hippocampus. 5. Given differences in habitat preference among benthic marine fishes subject to incidental capture in fisheries, simultaneous attempts to manage populations of sympatric species may require complementary strategies that support the persistence of diverse habitat types. Copyright (c) 2006 John Wiley & Sons, Ltd.

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.