Partial fishing mortality per fishing trip: a useful indicator of effective fishing effort in mixed demersal fisheries

Abstract

Effort management has been proposed as an alternative for quota management in mixed demersal fisheries. It requires a metric to estimate the fishing mortality imposed by a given quantity of nominal fishing effort. Here, we estimate the partial fishing mortality rate imposed by one unit of fishing effort (Fpue) during individual fishing trips and explore the usefulness of this indicator for managing North Sea beam trawlers >300 hp targeting sole (Solea solea) and plaice (Pleuronectes platessa). Fpue is positively related to vessel engine power, and increased annually by 2.8% (sole) and 1.6% (plaice). The positive trend was due to an increase in skipper skills and investment in auxiliary equipment, the replacement of old vessels by new ones and, to a lesser extent, to upgrade engines. The average Fpue imposed per day at sea by a 2000 hp beam trawler was estimated to be 1.0 × 10−5 (sole) and 0.6 × 10−5 (plaice), and it showed substantial seasonal and spatial variations. The Fpue of sole and plaice were negatively related in summer and showed no relationship in winter. The existence of predictive seasonal and spatial patterns in Fpue opens up the possibility of fine-tuning management by directed effort restrictions and uncoupling management of plaice and sole.

Long-term trajectory of some elasmobranch species off the Tuscany coasts (NW Mediterranean) from 50 years of catch data

“…Though long time series of data have been collected in the Atlantic and North Sea (e.g. many fish stocks in the North Atlantic, Rijnsdorp et al 2006), fisheries time series in the Mediterranean usually cover the last few decades only, and current management advice is based on data starting at best in the early 1990s (see Cardinale et al 2010). Therefore, the availability of 50-year series of fisheries data should be regarded as an almost unique opportunity to counteract a shifting baseline in fisheries management.…”

“…(Lindebo et al 2007, van Oostenbrugge et al 2008, Cardinale et al 2009). Fishing power growth has been estimated in different trawl fisheries and can range between 1.6 and 2.8% per year for beam trawls targeting sole and plaice in the North Sea (Rijnsdorp et al 2006), 0.6 and 3.1% for prawn fisheries in Australia (O'Neill and Leigh 2007) and up to 10% for Australian northern prawn fisheries (Ellis and Wang 2006). In the Mediterranean there are no correction factors taking into account this change, so it was decided to use an approach similar to that provided by Cardinale et al (2009) to correct the two data sets.…”

Ecological and economic trade-offs in the management of mixed fisheries: a case study of spawning closures in flatfish fisheries

“…The rationale for pooling the data by month and area is that we were interested in ALKs that are representative for the seasonal and spatial variations during the 5 yr study period. The fishing areas reflect the spatial distribution of sole and plaice in relation to management and are similar to a previous study (Rijnsdorp et al 2006). These month × area ALKs were subsequently applied to the catch-weight per market category per fishing trip ex tracted from the catch and effort data.…”

“…For each of the target species, the catchability generated during individual fishing trips in a certain area and week was estimated from the partial fishing mortality per day at sea (Fpue, where pue = per unit effort) following Rijnsdorp et al (2006): (1) where c ijk is the number of fish landed by vessel i in week j of age k, d ij is the number of days at sea of vessel i in week j, and c k is the total number of age k landed by the Dutch fleet. F k is the annual fishing mortality of age k by the entire international fleet.…”

Conservation value of historical data: reconstructing stock dynamics of turbot during the last century in the Kattegat-Skagerrak

“…Increasing catching efficiency (known also as technological creep or, simply, creep) of the fleet is usually positively related to the increase in skipper skills, investments in auxiliary equipment and more efficient gear and materials, replacement of old vessels by new ones and, to a lesser extent, upgraded engines (Rijnsdorp et al 2006). Creep has been estimated to be around 1.6 to 2.8% per year for the beam trawl fishery targeting sole and plaice in the North Sea (Rijnsdorp et al 2006), 0.6 to 3.1% for the prawn fisheries in Australia (O'Neill & Leigh 2007) and up to 10% for Australian northern prawn fisheries (Ellis & Wang 2006). Creep has been seldom estimated for surveys, although it is also known to occur in this case (Engelhard 2008).…”