Changes in the abundance and spatial distribution of the Atlantic chub mackerel (<i>Scomber colias</i>) in the pelagic ecosystem and fisheries off Portugal

Abstract

SUMMARY: This study describes changes in abundance and spatial distribution of Atlantic chub mackerel in the Portuguese waters and the Spanish waters of the Gulf of Cadiz using data from acoustic surveys from 1995 to 2010 and data from the fishery since 1958. The distribution and dynamics of chub mackerel and sardine (Sardina pilchardus) are compared and species interactions are discussed. From 2007 to 2009, chub mackerel biomass, as measured acoustically, ranged between 69000 and 238000 t concentrated off the western coast (~50%) and in the Gulf of Cadiz (~30%). Portuguese landings have varied with periods of high landings around 1970 and in recent years. Since 1986 landings have been between 4000 and 23000 t. Both survey catches and commercial landings are taken mainly off the southwestern coast and one-to two-year-old individuals (20-24 cm) predominate in both. Scarcity of larger individuals may be a consequence of their deeper distribution and avoidance of fishing gear, migration of older individuals or a combination of both. In years with high abundance, the fishery expands to the northwestern areas of the Iberian Peninsula. The expansion appears to be caused by improved recruitment although other factors might have contributed (such as targeting to compensate for low sardine catches and the appearance of new markets). The complementary spatial distribution of chub mackerel and sardine and the inverse correlations between their frequency of occurrence, landings and recruitment indices suggest some interaction between the dynamics of the two species, possibly associated with climatic variation.Keywords: Chub mackerel, sardine, Portugal, pelagic ecosystem, purse seine fishery. RESUMEN: Cambios en la abundancia y distribución espacial del estornino del Atlántico (Scomber coliaS) en el ecosistema pelágico y pesquerias de Portugal. -Este estudio describe los cambios en la abundancia y distribución espacial del estornino del Atlántico en las aguas portuguesas y aguas españolas del golfo de Cádiz a partir de datos de las prospecciones acústicas 1995-2010 y datos de la pesquería desde 1958. La distribución y la dinámica del estornino y de la sardina (Sardina pilchardus) se comparan y se analiza la interacción de las especies. Durante 2007-2009, la biomasa del estornino medida acústicamente osciló entre 69 y 238 mil t y se concentró frente a la costa occidental (~50%) y en el golfo de Cádiz (~30%). Los desembarques portugueses han variado con períodos de altas capturas alrededor de 1970 y en los últimos años. Desde 1986 los desembarques han sido entre 4 y 23 mil t. Ambas capturas de campañas y desembarques comerciales se toman principalmente en la costa sur occidental y individuos de 1-2 años edad (20 a 24 cm) predominan en ambos. La escasez de individuos más grandes puede ser una consecuencia de su distribución más profunda y la evitación de las artes de pesca, la migración de los individuos mayores o una combinación de ambos. En los años de mucha abundancia, la pesquería se expande a las áreas occidentales norte d...

Feeding ecology of the common dolphin (Delphinus delphis) in Western Iberian waters: has the decline in sardine (Sardina pilchardus) affected dolphin diet?

“…For chub mackerel only, there was a significant regional difference in its dietary importance, with higher numbers of this prey consumed in the southern area. This is consistent with higher estimated biomass and landings of chub mackerel in southern Portugal (Martins et al 2013, ICES 2016. This last observation gives some insight into the plasticity of common dolphin foraging behaviour, which not only demonstrates selection for favoured prey (sardine) and size-based selection, but also an element of opportunistic foraging, namely a diet composition which reflects regional abundance of prey.…”

“…In order to remain economically viable, the fishing sector has since been forced to target other pelagic species, namely Atlantic chub mackerel, Scomber colias, and horse mackerel, Trachurus trachurus. Both species have recently shown increased biomass off the Portugal-Cadiz region and, for chub mackerel, especially an inverse relationship with abundance of sardine has been found (Martins et al 2013, ICES 2016.…”

Which are the best environmental conditions for catching the beach‐seine target species? A Portuguese case study

“…The catches of small pelagic fish in the period under review (2007–2017) presented distinct trends: sardine and Atlantic horse mackerel showed a decreasing trend in catches while Atlantic chub mackerel showed an increasing pattern. The apparent switch from sardine to Atlantic chub mackerel catches could be related with an inverse correlation between the recruitment indices of the two species (Martins, Skagen, Marques, Zwolinski, & Silva, 2013), which could result from competition for food, predation or different response of each species to the same environmental conditions, because the fact that different species have different tolerance to abiotic factors (temperature, salinity).…”

Situação ecológica, socioeconómica e de governança após a implementação do primeiro plano de ordenamento no Parque Marinho Professor Luiz Saldanha (Arrábida, Portugal): I – informações e opiniões dos pescadores

“…• Existem algumas indicações de alterações para espécies não alvo, com os pelágicos a aumentar e a faneca a diminuir, que são corroboradas pelos dados de desembarques nos últimos anos (no caso dos pelágicos mesmo para embarcações locais fora do PMLS) e, no caso da cavala por literatura recente (e.g. Martins et al, 2013);…”