Inter- and intra-annual trends and status indicators of nektobenthic elasmobranchs off the Balearic Islands (northwestern Mediterranean)

Abstract

SUMMARY:We assessed the elasmobranch communities exploited by the bottom trawl fishery off the Balearic Islands (northwestern Mediterranean) by analysing two time series containing information with different levels of detail: 1) a longterm series containing the abundance indices of the whole elasmobranch community landed from 1965 to 2009; and 2) a shorter time series from 2000 to 2009 from two different data sources (daily sales records: 2000-2009; bottom trawl surveys: 2001-2009), with information that allowed the shelf and slope to be analysed separately and different community parameters and abundance indices to be studied. Temporal trends of all these variables were used as ecological status indicators and tested with generalized additive models and analysis of variance. They were finally summarised using the Traffic Light methodology. The long-term series showed two marked trends, an inter-annual decreasing trend that would be a consequence of the large increase in fishing effort, and an intra-annual trend with a clear peak in May in accordance with the seasonal biological cycle of these species. However, data from the last ten years revealed differences between the shelf and slope, as some parameters increased significantly over time on the shelf but did not follow any trend on the slope. The Traffic Light methodology captured these differences well, demonstrating its usefulness for interpreting ecological transitions at a glance.Keywords: elasmobranchs, assessment, Traffic Light method, indicators, fishing effort, Balearic Islands. RESUMEN:Tendencias inter e intra-anuales e indicadores del estado de las poblaciones de elasmobranquios nectobentónicos de las Islas Baleares (Mediterráneo nordoccidental). -Se han evaluado las poblaciones de elasmobranquios explotadas por la pesca de arrastre de las Islas Baleares (Mediterráneo noroccidental) analizando dos series temporales con información a distinto nivel de detalle: 1) una serie larga que contiene únicamente el índice de abundancia de toda la población de elasmobranquios desembarcada entre 1965 y 2009 y 2) una serie corta a lo largo de la primera década del siglo XXI proveniente de dos fuentes de datos diferentes (hojas de venta diarias: 2000-2009; campañas de arrastre de fondo: 2001-2009), que permitieron el análisis, para la plataforma y el talud por separado, de diferentes parámetros de la comunidad además de índices de abundancia. Las tendencias temporales de todas estas variables se usaron como indicadores ecológicos de estado y se testaron aplicando modelos generales aditivos y análisis de la varianza y finalmente se han resumido usando la metodología de los Semáforos. La serie larga mostró dos señales claras, un decrecimiento interanual que podría ser consecuencia del importante incremento del esfuerzo pesquero, y una tendencia intra-anual con un claro pico en mayo, relacionado con el ciclo biológico estacional de estas especies. Así y todo, los datos del primer decenio del siglo XXI revelaron diferencias entre la plataforma y el talud, porque algu...

Demersal chondrichthyans in the western Mediterranean: assemblages and biological parameters of their main species

“…Benthic communities are considered highly productive and sensitive habitats and are distributed widely on the trawl fishing grounds of the shallow and deep shelf off the Balearic Islands respectively. Furthermore, displacement of the trawling effort from the shelf to the slope during the past decade, targeting the most vulnerable fishing resource in this area, namely the red shrimp Aristeus antennatus, has been argued by Guijarro et al (2012) to explain the slight recovery detected during recent years in the elasmobranch populations on the CS of this archipelago, which has not been observed on the slope.…”

Spatial variability of Chondrichthyes in the northern Mediterranean

“…-Number of MEDITS hauls carried out annually during the period 2012-2015 and analysed in the present study by geographical sub-area (GSA) of the General Fisheries Commission for the Mediterranean, country and depth strata (total, 10-800 m; continental shelf, 10-200 m; slope, 201-800 m). Area Total hauls Shelf hauls Slope hauls 1 Spain Northern Alboran 187 71 116 5 Spain Balearic Islands 218 142 76 6 Spain Northern Spain 388 282 106 7 France Gulf of Lions 66 55 11 8 France Corsica 23 10 13 9 Italy Ligurian, northern and central Tyrrhenian seas 120 55 65 10 Italy Central and southern Tyrrhenian seas 70 29 41 11 Italy Sardinian seas 101 63 38 16 Italy Strait of Sicily 120 55 65 17 Italy ish (Guijarro et al 2012, Barría et al 2015, Ramírez-Amaro et al 2015, Italian (Follesa et al 2011, Ligas et al 2013, Marongiu et al 2017 and Greek waters (Maravelias et al 2012, Tserpes et al 2013). These studies have been carried out on the northern Mediterranean coast and very few have been carried out on the southern coast off Africa (e.g.…”

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).…”