Joaquim Ribeiro

Weight-length relationships for selected fish species of the small-scale demersal fisheries of the south and south-west coast of Portugal

Abstract Weight-length relationships were estimated for 31 fish species from the south and south-west coasts of Portugal. These species, which are mainly sea breams (Sparidae), dominate the catches of the main fixed gears used in this region and account for more than 50% and 40% of the total fish landings by weight and by value.

Quantifying recreational shore angling catch and harvest in southern Portugal (north-east Atlantic Ocean): implications for conservation and integrated fisheries management.

Recreational shore fishing along 250 km of the south and south-west coast of Portugal was studied based on roving creel and aerial surveys. Surveys were conducted between August 2006 and July 2007, following a stratified random-sampling design and provided information on catch and effort, harvest and discards, angler demographics and fishing habits. Overall, 192 roving creel surveys, 24 aerial surveys and 1321 interviews were conducted. Based on the aerial surveys, a mean +/-s.e. total fishing effort of 705,236 +/- 32,765 angler h year(-1) was estimated, corresponding to 166,430 +/- 9792 fishing trips year(-1). Average time spent per fishing trip was 4.7 h. A total of 48 species, belonging to 22 families, were recorded in roving creel surveys. The most important species was Diplodus sargus, accounting for 44% of the total catches by number and 48% by mass. Estimated mean +/-s.e. total annual recreational shore fishing catch was 160.2 +/- 12.6 t year(-1) (788,049 +/- 54,079 fishes year(-1)), of which 147.4 +/- 11.9 t year(-1) (589,132 +/- 42,360 fishes year(-1)) was retained. Although overall shore-based recreational catches only corresponded to 0.8% of the commercial landings (only common species considered), D. sargus catches by recreational shore anglers were considerable, corresponding to 65% of the commercial landings. The implications of these results for integrated fisheries management and conservation are discussed, and future research proposed.

Species and size selectivity in a 'red' sea bream longline 'metier' in the Algarve (southern Portugal)

A longline ‘metier’ using small hooks for ‘red’ sea breams (Pagellus acarne and Pagellus erythrinus) in the Algarve (south of Portugal) was studied. Experimental longlining was carried out with three sizes of “Mustad” round bend, flatted, spade end Quality 2316 DT hooks (numbers 11, 13 and 15) and two types of bait: razor shell (Ensis siliqua) and mud shrimp (Upogebia pusilla). A total of 3 328 fish and at least 36 species were caught with 33 600 hooks fished in 28 longline sets. Five species of sea breams (Sparidae) accounted for 79% of the catch: Pagellus acarne, Pagellus erythrinus, Diplodus vulgaris, Spondyliosoma cantharus, and Boops boops. High catch rates of 20–30 fish per 100 hooks were made in a number of 1 200 hook longline sets, with total catch weights of 40 to more than 60 kg per set. In general, the smallest hook (number 15) had the highest catch rate. Bait type did not significantly affect the catch size distributions. Although more fish were caught with the razor shell bait, higher catch rates of ‘red’ sea breams were obtained with mud shrimp. Catch rates were also affected by the location of the fishing grounds and the time of the set, with the highest catch rates obtained when the longline was set within two hours before sunrise. A wide size range was caught for each species, with highly overlapped catch size frequency distributions for the three hook sizes used. Except for Spondyliosoma cantharus, few illegal-sized fish were caught, even with the smallest hook. The logistic model fitted by maximum likelihood was used to describe hook selectivity for Diplodus vulgaris, Pagellus acarne, Pagellus erythrinus, and Spondyliosoma cantharus.

Age and growth, maturity, mortality and yield-per-recruit for two banded bream (Diplodus vulgaris Geoffr.) from the south coast of Portugal

The population dynamics parameters of Diplodus vulgaris(Sparidae) from the south and south-west coast of Portugal were studied. 1086 fishes with total lengths ranging from 3.3 to 37.9 cm were obtained from previous gear selectivity studies supplemented by market sampling and beach seining for juveniles (1992–2000). The spawning season extended from September to April and total lengths at 50% maturity were 17.27 cm for males and 17.65 cm for females. These estimated sizes were greater than the minimum legal landing size (MLS = 15 cm) and smaller than length at first capture (Lc 50 = 21.68 cm) for the longline fishery. The parameters of the von Bertalanffy growth equation were: L∞ = 27.73 cm, K = 0.40 per year, t0 =− 0.34 year. The instantaneous rates of total mortality ( Z) and natural mortality (M) were 0.63 and 0.45 per year, respectively. Rates of fishing mortality F and exploitation E were 0.18 and 0.28 per year, respectively. Estimated parameters and the relative yield-per-recruit analysis showed that this species is not over exploited by longlines.

Life history of the common pandora, Pagellus erythrinus (Linnaeus, 1758) (Actinopterygii: Sparidae) from southern Portugal

A bica, Pagellus erythrinus, e uma especie comercialmente importante para as pescarias costeiras do norte e centro este Atlântico. A idade, crescimento e aspectos reprodutivos da populacao que ocorre no sul de Portugal foram estudados atraves da analise de 386 exemplares com comprimentos totais (TL) entre 12.0 e 44.8 cm. A idade foi estimada pela contagem de bandas de crescimento nos otolitos e verificada pela analise do incremento marginal, tendo-se observado exemplares entre os 1 e 21 anos. A curva de crescimento de von Bertalanffy foi o modelo mais adequado para explicar o crescimento desta especie, tendo estimado Linf = 47.14 cm TL, k = 0.084 ano-1 e t0 = - 4.42 ano. As gonadas foram analisadas macroscopicamente ao longo do periodo de um ano e determinou-se que a desova ocorre entre Marco e Julho. A primeira maturacao dos machos ocorre aos 17.58 cm TL e 1.15 anos enquanto as femeas maturam com tamanhos (17.29 cm TL) e idades (1.04 anos) ligeiramente menores. Os resultados apresentados sao importantes para a comparacao desta populacao com populacoes de outras regioes, assim como para a comparacao com estudos futuros, para a determinacao de eventuais alteracoes nos parâmetros populacionais ao longo do tempo.

Age and growth, mortality and reproduction of the striped sea bream, Lithognathus mormyrus Linnaeus 1758, from the south coast of Portugal (Algarve)

Abstract The striped sea bream, Lithognathus mormyrus, used for this population dynamics study were obtained from longline catches and market sampling in the Algarve (south Portugal). The macroscopic analysis of the gonads and the gonad somatic index showed that the south Portuguese population of L. mormyrus spawns mainly between late spring and summer (June to August). The length at first maturity was similar for males and females and the value for both sexes combined was estimated to be 16.08 cm, corresponding to an age between 1 and 2 years. Fish age classes (0 to 13) were determined by reading growth rings on whole otoliths. Age determination was validated by marginal increment analysis. The estimated parameters of the von Bertalanffy growth equation were L∞=35.30 cm, K=0.264 and t 0= − 0.809. Mortality rates were calculated for fish captured with longlines, and the estimated parameters were M=0.356, Z=0.622 and F=0.266. From an Algarve fishery management perspective, these results suggest the need for an increase in the minimum landing size (from 15 to 17 cm), which should be beneficial for the sustainability and conservation of this species. The results also showed that fishing with longlines off the Algarve coast may allow for a sustainable use of the resource.