Assessment of the deep water trawl fishery off the Balearic Islands (western Mediterranean): from single to multi-species approach

Abstract

The bottom trawl fishery developed on the slope off Balearic Islands (western Mediterranean) has been analysed from different sources of information: (i) data obtained during experimental bottom trawl surveys developed annually since 2001; (ii) daily sale bills from the bottom trawl fleet, available since 2000. Considering both hydrographical and geomorphologic conditions, the study area was divided in four geographical sectors. Multivariate techniques were applied to identify assemblages and their main species, and to investigate the influence of environmental variables in the slope communities. Fishery-independent and fisherydependent indicators were calculated, both at specific and community level, for the assemblages identified. In all cases, they were summarised using the Traffic Light approach. Three assemblages have been identified in the slope trawl fishing grounds off the Balearic Islands: (1) the almost unexploited shelf break, where teleosts predominate; (2) the upper slope, where teleosts still predominate but crustaceans are also very important (with Nephrops norvegicus as target species); (3) and the middle slope, where crustaceans predominate (with Aristeus antennatus as target species). Depth was the main factor affecting the species composition of the assemblages, although other factors such as area, year and effort level also affect. Indicators estimated from both sets of data suggested an improvement in the state of N. norvegicus, although the results suggest the influence of other factors than fishing impact in the state of this resource. For A. antennatus, marked differences have been found depending on the data source. In the upper slope, indicators suggested an improvement in the state of this assemblage, which can be related to a decreasing trend found in the fishing effort exerted in this depth range. Indicators from the middle slope showed differences for both sets of data. The characteristics of both data sources and of the species analysed are discussed as responsible of these differences.

Climate and grazing control nurse effects in an Ecuadorian dry shrubby community

“…Measures were recorded each minute between January 2010 and December 2011. We built a climatic diagram (Walter & Lieth 1960) using the package climatol implemented in R environment (Guijarro 2011). Around 80% of precipitation was recorded between February and March (Figure 1).…”

Harvest Strategies for an Ecosystem Approach to Fisheries Management in Western Mediterranean Demersal Fisheries

“…Assessing the complexity of exploited ecosystems using a variety of indicators demands the use of summarizing approaches such as the traffic lights methodology, which has already been used in the Balearic Islands (Guijarro et al, 2011(Guijarro et al, , 2012b. This approach was firstly proposed as a type of precautionary management framework suitable for use in fishery assessment in data-poor situations (Caddy, 2002), but it can also be used to assess the status of all stocks whether rich or poor in data (Halliday et al, 2001).…”

Large-scale distribution of a deep-sea megafauna community along Mediterranean trawlable grounds

“…elasmobranchs and non-crustacean invertebrates). High values of crustacean density have been related to medium and high levels of fishing effort (Guijarro et al 2011) and, in fact, high catches of A. antennatus have been related to the ability of fishermen to remove competitors at a higher rate (Sardà and Maynou 1998). Interestingly, the only exception was the Alboran Basin (GSA 1 and 2) where the community was dominated by Chondrichthyes.…”

“…Mediterranean deep-water fisheries began in the first decades of the last century, coinciding with the development of new technologies that made fisheries in deeper waters possible (Relini and Orsi Relini 1987, Spedicato et al 1995, Sardà and Demestre 1987. Larger vessels with more powerful winches and stronger cables were increasingly used from Mediterranean harbours (Farrugio et al 1993, Guijarro et al 2011, Quetglas et al 2017. Two main deep-sea bottom fisheries have extended along the Mediterranean continental slope: (i) an upper slope (~200-600 m) fishery targeting Nephrops norvegicus and Parapenaeus longirostris, and ii) a middle slope (~400-800 m) fishery targeting Aristaeomorpha foliacea and Aristeus antennatus (Sardà et al 2004a).…”