CAUSAS DE JUSTIFICACIÓN EN EL DELITO DE HOMICIDIO

The efficacy of marine protected areas (MPAs) as a management tool for conservation is dependent on appropriate design and management measures (Agardy 1994; Agardy 2000). In the designation of an MPA, boundaries will typically be placed using the static factors that help explain a species distribution, providing a biological rationale for the spatial limits of an MPA. However this may not be the best design, as species distribution may vary temporally depending on fluid environmental characteristics as well as the movements and abundance of prey species and the potential for breeding (during certain periods) (Wilson et al. 2004). Consequently, it is crucial to have an accurate knowledge of the target species’ distribution and whether its habitat usage is subject to significant temporal variations (Agardy 1994; Cañadas et al. 2005; Hooker et al. 1999; Rayment et al. 2010) so that the spatial (and possibly temporal) boundaries of a protected area can evolve with improving knowledge, to ensure appropriate management for the species.

Many cetacean species have been found to exhibit seasonal changes in distribution and/or behaviour (Ballance et al. 2006; Baumgaertner and Mate 2005; Cañadas and Hammond 2008; Forney and Barlow 1998; MacLeod et al. 2004; Mattila and Clapham 1989; Moore et al. 2000; Neumann 2001; Northridge et al. 1997; Reilly 1990; Siebert et al. 2006; Tynan et al. 2005; Walker 1996; Weir et al. 2007). The best studied seasonal movements are the long, annual migrations that a number of baleen whales species make between profitable feeding grounds and appropriate breeding/calving grounds (Jones and Swartz 2002; Payne 1983; Whitehead and Moore 1982). Other species make intra-annual inshore/offshore movements, most likely to take advantage of meso- and macro-scale shifts in prey distribution (Cañadas and Hammond 2008; Neumann 2001) and similar intra-annual shifts have been observed in dolphin species around the UK (Northridge et al. 1995; Wilson et al. 1997).

Seasonal changes in distribution may also be accompanied by a shift in acoustic behaviour. For example, Jacobs et al. (1993) documented a change in bottlenose dolphin vocal behaviour between summer and autumn months, attributing a doubling in vocalisation rates to a shift from mostly socialising behaviour during the summer, to mainly foraging during the autumn. A similar pattern has been observed in bowhead whales with increased vocalisation rates and a wider vocal repertoire being employed during spring compared with during the winter periods (Tervo et al. 2009).

A number of studies have observed seasonal shifts in harbour porpoise distribution and/or occurrence (Gilles et al. 2009; Northridge 1995; Siebert et al. 2006; Teilmann et al. 2008; Verfuß et al. 2007). Northridge (1995) observed, from aerial survey data collected between 1978 and 1988 in the Gulf of Maine, that animals were generally more dispersed across the region in June than in April and May. Additionally, they observed that animals were aggregated in the northern of the area during July - September (Northridge 1995). Incidental sightings and strandings data collected over a decade in the German Baltic and North Seas revealed a ‘strong seasonality’ in harbour porpoise occurrence with the highest numbers in during July and August (Siebert et al. 2006). However, methods used in that study had some biases in the data

collection, in that there was unequal sightings effort and differing lengths of time of submersion for the stranded carcasses. A study using porpoise echolocation data loggers (T-PODs) observed a significant increase in porpoise positive days in July – September when compared with activity in January – March, whilst observing that porpoises were present throughout the year in the region (Verfuß et al. 2007). Gilles et al. (2009) conducted aerial surveys in the German North Sea to further investigate annual habitat usage patterns. They observed that porpoises moved into ‘distinct areas’ in spring months, with peak encounter rates in May and June. This suggests that in this region animals become more evenly dispersed in the autumn months, with this dispersion starting in September (Gilles et al. 2009). Teilmann et al. (2008) used a combination of satellite tagging, aerial surveys and shipboard surveys to investigate high-density regions and found seasonal variability in the relative importance of particular regions in waters in Denmark. Harbour porpoises have been observed around Scotland throughout the year, though there have been higher encounter rates recorded in summer months (Evans et al. 2003; Reid et al. 2003; Weir et al. 2007). Weir et al. (2007) investigated harbour porpoise distribution off the east coast of Scotland and observed that porpoises were present throughout the year. No animals were detected in January and February but detection rates generally increased from March, peaking in August and September, before decreasing in October (Weir et al. 2007).

While a number of studies have observed seasonal changes in distribution and/or occurrence, very few studies exist that have investigated seasonality in habitat preferences in harbour

porpoises. A study in the Bay of Fundy included an intra-annual measure in the form of ‘lateness of season’ when investigating habitat preferences of harbour porpoises (Watts and Gaskin 1985). However, it was found that it was not significantly correlated with mean sighting frequency. A study in the eastern Pacific Ocean documented shifts in habitat preferences in harbour porpoises between the spring (May and June) and summer (July and August)(Tynan et al. 2005). Animals were more commonly associated with high-salinity upwelled water during the spring months, which occurred close to shore. In summer, animals were found further offshore, once again correlating strongly with the location of an upwelling which had shifted (Tynan et al. 2005). In an earlier analysis using some of the data used in this study and different analytical methods, porpoise habitat preferences and distribution were investigated on the west coast of Scotland (Embling 2007; Embling et al. 2010). Month was not retained in the best models, indicating that in that analysis it was not a significant factor impacting porpoise detection rates in those models. Other studies of harbour porpoises habitat preferences have data collected over a limited time period or have not included month as a covariate in the analysis (Bailey and Thompson 2009; MacLeod et al. 2007; Marubini et al. 2009).

In Chapter 3 I investigated the inter-annual variations in harbour porpoise habitat preferences and distribution on the west coast. I found when investigating the full models, that there was significant intra-annual variation in porpoise detection rates, as ‘month’ was retained in both the best visual and acoustic models (§3.3.1 and §3.3.2). In this study, I investigated intra-annual variations in harbour porpoise distribution and habitat preferences off the west coast of Scotland by building individual monthly and seasonal models (using a pooled six-year dataset). The key aims of this work were: (i) determine whether clear monthly or seasonal shifts in distribution and habitat preferences exist in this region and if so (ii) to determine if any intra-annual patterns need to be considered in a protection framework for harbour porpoises in this region. This work is ultimately aimed at improving knowledge of harbour porpoise distribution and habitat usage off the west coast of Scotland to inform future conservation and management efforts.