A comparison of direct macrofaunal mortality using three types of clam dredges

Gaspar, Miguel B.; Leitao, F.; Santos, Miguel N.; Chı́charo, Luis; Dias, Maria Djair; Chícharo, Alexandra; Monteiro, Carlos C.

doi:10.1016/s1054-3139(03)00023-7

Cited by 48 publications

(36 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In brief, the dredge weighs around 40 kg and consists of a rigid iron structure with a toothed lower bar (15 cm tooth length with an angle of 208). The catch is retained in a net bag 2.5 m long with diamond mesh size of 25 mm for further details on the dredge design, characteristics and dimensions, see (Gaspar et al 2003); (Leitão et al 2009). …”

Section: Methodsmentioning

confidence: 99%

Age and growth in three populations of Dosinia exoleta (Bivalvia: Veneridae) from the Portuguese coast

2013

View full text Add to dashboard Cite

The present study aimed at estimating the age and growth in three populations of Dosinia exoleta from the Portuguese coast (Aveiro in the north, Setúbal in the southwest and Faro in the south). Two techniques were compared to ascertain the most suitable method for ageing D. exoleta. Growth marks on the shell surface and acetate peel replicas of sectioned shells were the techniques applied. Two hypotheses were tested: growth parameters present latitudinal variation along the Portuguese coast; growth parameters are influenced by the fishing exploitation. Shell surface rings proved inappropriate for ageing this species, whereas acetate peels provided realistic estimates of the von Bertalanffy growth parameters (K, L ? and t 0 ). A latitudinal gradient in growth rate was detected, with a clear southward increase in the growth coefficient (K) of D. exoleta (Faro [ Setúbal and Aveiro) indicating that warmer waters in southern Portugal provide optimal conditions for the growth of this species. Fishing exploitation in northern Portugal targets larger individuals and leaves behind a younger population of smaller individuals, decreasing the asymptotic shell length (L ? ) of D. exoleta from Aveiro. The overall growth performance was compared among populations of D. exoleta and with other venerid species worldwide.

show abstract

Section: Methodsmentioning

confidence: 99%

Age and growth in three populations of Dosinia exoleta (Bivalvia: Veneridae) from the Portuguese coast

2013

View full text Add to dashboard Cite

show abstract

“…The most recent modification to the dredge design included the adoption of a metallic grid box to retain the catches above the target species minimum landing size (MLS), by filtering out smaller individuals of both target and non-target species. Though it is more efficient and selective than previous dredge designs (Gaspar et al 2001, 2003a, Leitão et al 2009), in some periods of the year the amount of bycatch collected by this gear can exceed the catch of the target species, especially in late spring and early summer (Gaspar and Chícharo 2007).…”

Section: Introductionmentioning

confidence: 99%

“…The mode of operation and technical design of mechanized dredges have undergone gradual developments thanks to studies aimed at improving dredge selectivity (Gaspar 1996 and reducing catch mortality , Gaspar et al 2003a, Leitão et al 2009). The most recent modification to the dredge design included the adoption of a metallic grid box to retain the catches above the target species minimum landing size (MLS), by filtering out smaller individuals of both target and non-target species.…”

Section: Introductionmentioning

confidence: 99%

Bycatch and discard survival rate in a small-scale bivalve dredge fishery along the Algarve coast (southern Portugal)

et al. 2018

View full text Add to dashboard Cite

Summary:Although the bivalve dredge used on the Algarve coast (southern Portugal) is highly selective for the target species, in some periods of the year the bycatch can exceed the catch of the commercial species. The present study aimed to quantify the bycatch and discards, estimate damage and mortality, and propose management measures to minimize discards and mortality. A total of 15 fishing surveys (60 tows) were performed using two types of dredges ("DDredge" targeting Donax trunculus and "SDredge" targeting Spisula solida and Chamelea gallina). Of the 85257 individuals (392.4 kg) of 52 taxa that were caught, 73.4% belonged to the target species, 22.1% to commercially undersized target species and 4.5% to bycatch species. Bycatch rates were lower for SDredge (13.5% in number and 6.3% in weight) than for DDredge (46.0% in number and 32.9% in weight). Damage and mortality rates were also lower using SDredge (1.3% and 1.0% of the total catches, respectively) than using DDredge (4.0% and 2.8% of the total catches). Survival experiments revealed the diverse vulnerability of the taxa and confirmed the influence of the damage score on the mortality rate. The results gathered in the present study encourage the adoption of a bycatch reduction device to reduce both direct and indirect mortality.Keywords: bivalve dredging; bycatch; discards; damage score; survival rate; metallic grid dredge; fishing gear technical design; bycatch reduction device Tasa de supervivencia de capturas incidentales y descartes en una pesquería a pequeña escala de bivalvos con rastro remolcado en la costa del Algarve (sur de Portugal) Resumen: Aunque la draga de bivalvos utilizada en la costa del Algarve (sur de Portugal) es altamente selectiva para las especies objetivo, en algunos períodos del año la captura incidental puede exceder la captura de las especies comerciales. En este contexto, el presente estudio tuvo como objetivo cuantificar las capturas incidentales y los descartes, estimar el daño y la mortalidad, y proponer medidas de gestión para minimizar los descartes y la mortalidad. Se realizaron un total de 15 embarques (60 arrastres) utilizando dos tipos de dragas ("DDredge" dirigida a Donax trunculus y "SDredge" dirigida a Spisula solida y Chamelea gallina). En total, se capturaron 85257 individuos (392.4 kg) pertenecientes a 52 taxones, distribuidos entre especies objetivo (73.4%), especies objetivo por debajo de la talla legal (22.1%) y especies de captura incidental (4.5%). Las tasas de captura incidental fueron menores en SDredge (13.5% número y 6.3% peso) que en DDredge (46.0% número y 32.9% peso). Las tasas de daños y mortalidad también fueron menores usando SDredge (1.3% y 1.0% de las capturas totales) que usando DDredge (4.0% y 2.8% de las capturas totales). Los experimentos de supervivencia revelaron la diferente vulnerabilidad de los taxones y confirmaron la influencia del nivel de lesiones en la tasa de mortalidad. Los resultados del presente estudio fomentan la adopción de un dispositivo de reducción de capturas inciden...

show abstract

“…Spisula solida is one of the most harvested species in Algarve coast, where an important clam dredge fishery takes place Chícharo et al, 2002a,b;Palma et al, 2003). The dredges are designed to dig clams out of the sediment, disturbing the seabed both in terms of physical structure and biological communities (Gaspar et al, 2003). Besides the impact on the S. solida populations, these fisheries may also have impacts on other non-target species, such as the hermit crabs, which frequently constitute the by-catch of these fisheries (Gaspar et al, 2002(Gaspar et al, , 2003Palma et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

“…The dredges are designed to dig clams out of the sediment, disturbing the seabed both in terms of physical structure and biological communities (Gaspar et al, 2003). Besides the impact on the S. solida populations, these fisheries may also have impacts on other non-target species, such as the hermit crabs, which frequently constitute the by-catch of these fisheries (Gaspar et al, 2002(Gaspar et al, , 2003Palma et al, 2003). Hermit crabs do not seem to be strongly affected by injuries caused by the dredges (Gaspar et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Population structure and species dynamics of Spisula solida, Diogenes pugilator and Branchiostoma lanceolatum along a temporal–spatial gradient in the south coast of Portugal

Dolbeth¹,

Viegas²,

Martinho³

et al. 2006

Estuarine, Coastal and Shelf Science

View full text Add to dashboard Cite

The population structure, dynamics and distribution of Spisula solida, Diogenes pugilator and Branchiostoma lanceolatum, common species in the south coast of Portugal, were studied in a spatialetemporal manner in order to understand the influence of cross-shore sediment transport and anthropogenic activities. Spisula solida is harvested commercially, whereas D. pugilator and B. lanceolatum are non-target species, with little information available on the population dynamics of these species. The study was performed in 2001e2002, and along a gradient of 100e5000 m from the coastline, corresponding to a depth gradient of between 1 and 32 m deep. Spisula solida was distributed preferentially at 3e12 m deep, and its distribution appeared to be influenced seasonally by the cross-shore sediment dynamics. Results suggested benthic recruitment in June. Some recruitments had no expression (year 2001) since adults were not present, which seems to be a direct impact of clams' fisheries. Diogenes pugilator showed preferential distribution at shallow depths, from 1.3 to 8 m. Results suggested recruitments every 4 months, in June, February and October. Branchiostoma lanceolatum showed the widest distribution, from 7 to 26 m deep. Recruitment seemed to start in June until October, when it attained an abundance peak of juveniles. For both non-target species no clear effects of the cross-shore dynamics or the clams' fisheries impact were visible.

show abstract

A comparison of direct macrofaunal mortality using three types of clam dredges

Cited by 48 publications

References 22 publications

Age and growth in three populations of Dosinia exoleta (Bivalvia: Veneridae) from the Portuguese coast

Age and growth in three populations of Dosinia exoleta (Bivalvia: Veneridae) from the Portuguese coast

Bycatch and discard survival rate in a small-scale bivalve dredge fishery along the Algarve coast (southern Portugal)

Population structure and species dynamics of Spisula solida, Diogenes pugilator and Branchiostoma lanceolatum along a temporal–spatial gradient in the south coast of Portugal

Contact Info

Product

Resources

About