Shannon dolphins prove alusive to tour boats during 2009 season
Dolphin Tour boat operators in the Shannon Estuary had a poor year in 2009 due to a combination of weather, poor tourist numbers but also a change in dolphin behaviour.
The SDWF think that a massive decline in salmon returning to the Shannon Estuary may be causing the dolphins to forage in new areas, including further afield off Lopp Head and in Tralee Bay to obtain sufficient food during the summer. The Shannon Regional Fisheries Board estimate a 75% decline in salmon to the estuary over the past two years.
Trips numbers and performance
Two companies, with one dolphin-watching vessel each, carried out dolphin-watching in the Shannon Estuary cSAC during 2009. The total reported number of trips (241) were 22% less than reported in 2008 with trips from Carrigaholt down by 10% and Kilrush by 33 %. Similarly to 2008, most trips were carried out in July, and not August due to bad weather during that month.
The ongoing trend is towards a decline in tour boat activity driven by poor weather during peak months (July and August) and a decline in tourism to west Clare.
Mean trip length increased from both Carrigaholt and Kilrush during 2009 to the highest recorded since monitoring began. It was particularly elevated (16.7%) from Kilrush. Mean time to locate dolphins also increased significantly, up 27% from Carrigaholt and 20% from Kilrush. The proportion of trips with no dolphins observed was also greater than in previous years. This resulted in the total time on dolphins being down 32% overall and a huge 52% by the Kilrush dolphin-watching boat.
There was a change in zones in which dolphins were located and watched, with an increase again observed to the south side of outer estuary. Following a decrease in 2008, there was an increase in trips to Beal bar. A decrease was recorded at the south side of the estuary with a corresponding increase to the outer estuary by the Kilrush operator.
Trends in monitoring indices
The results from monitoring during 2009 show large changes in the monitoring indices. This reflects a very poor season by dolphin-watching operators in the Lower River Shannon cSAC, who not only had to operate in a poor tourism season and poor weather, especially in August, but also struggled to find dolphins when conditions were good. This is evident from the increase in time to locate dolphins and length of dolphin trip. Changes in zones reflected boats, especially from Kilrush, having to search for dolphins outside of the areas they watched dolphins in recent years. It is not possible to identify the reasons why dolphins’ distribution was different during 2009 but there are indications that dolphins may be exploring different areas in the Shannon Estuary and adjacent waters presumably in which to forage. Bottlenose dolphins are now observed very frequently off Loop Head at the mouth of the Shannon (IWDG unpublished data) and were also recorded off Tralee and Brandon Bays during the summer of 2009 (Ryan and Berrow, in press). One explanation is changes in the numbers and timing of salmon in the estuary. Shannon Regional Fisheries Board reported a 50-60% decline in salmon entering spawning rivers during 2009 compared to 2008 which was down 50% from 2007. This equates to a decline of around 75% between 2007 and 2009: this decline in salmon numbers in the estuary may be forcing the dolphins to forage further afield (Loop Head, Tralee Bay) to obtain their daily food requirements. As 2007 was a good year for salmon returning to spawning rivers it is hoped that 2010 is a good year as most fish return after three years (SRFB pers. comm.). Monitoring dolphin prey such as salmon is essential if we are to understand changes in the distribution and behaviour of the Shannon dolphins.
This monitoring does provide a good reflection of changes in the dolphins’ distribution and also relative abundance. Small or subtle long-term changes to dolphin behaviour or distribution are hard to record as these signals are difficult to distinguish against inter-annual variations. A catastrophic event such as major changes to the population within the Shannon Estuary or the dolphins’ sensitivity to dolphin-watching boats will be identified. Bottlenose dolphins are long-lived animals with a generation time of around 20 years. Ten percent of those individual dolphins observed from dolphin-watching vessels during 2009 were also recorded from dolphin boats ten years earlier in 1999, demonstrating the importance of long-term monitoring. This monitoring also ensures the continued sustainable development of the dolphin-watching industry in a marine candidate Special Area of Conservation.
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Special Area of Conservation (SAC)