In the second part of our guest article, Dr Farrell discusses the progression of his research on starry smooth-hound (after clearing up the identification confusion!) and the implications his research might have on future management of smooth-hound populations in the north-east Atlantic.
Current Fishery and Management
Resolving the identification issues of Northeast Atlantic smooth-hounds greatly simplified the next part of the project by allowing us to focus our efforts on just one species, the starry smooth-hound. Despite the popularity of the species with anglers very little was known about its basic biology, particularly in the Northeast Atlantic. Based on old research in the Mediterranean, this species was previously considered to be a fast growing, early maturing (2.5 years) and productive species, which would mean that it is not a conservation concern. This may be one of the reasons that there are currently no management or conservation measures in place for this species.
Despite popular belief, smooth-hounds are a commercially valuable species and face significant fishing pressure. Large fisheries for smooth-hounds used to exist in the Mediterranean, however these peaked in 1994 when Italy reported landings of 9,999 tonnes and subsequently rapidly declined to about 450 tonnes by the start of the 21st century. The image below shows boxes of starry smooth-hound landed at Lorient fish market in Northern France.
Smooth-hounds have since been reported to be locally extinct or depleted in a number of areas of the Mediterranean including the Gulf of Lion, the Adriatic Sea and the Upper Tyrrhenian Sea and also in the Atlantic in the southern Bay of Biscay and in Portuguese waters. In Northern European waters smooth-hound stocks have been reported as stable or even increasing in some areas, which is great news.
They are however regularly taken as by-catch in mixed demersal fisheries and are usually discarded. Worryingly though, in France, Belgium and increasingly in the UK they are landed for the continental market where their flesh is highly valued. Reported landings of smooth-hounds from the Northeast Atlantic have been steadily increasing in France and are currently in the region of 2,500 tonnes per year. This may be a gross underestimate as the difficulties in identification prevent reliable landings data to be collated and they are generally just landed as ‘hounds NEI (not elsewhere identified)’ or even just as ‘dogfish NEI’. They are also often sold together in mixed boxes with Tope.
The recent introduction of restrictions on landing tope and spurdogs may result in a redirection of effort and put further pressure on smooth-hound stocks.
Without a sound knowledge of the biological characteristics of a species it is almost impossible to introduce effective management or conservation measures. This is the reason the second phase of the project was initiated with the specific aims of establishing the age and growth characteristics, the age- and length-at-maturity and also enhancing our knowledge of the reproductive cycle.
To this end 232 starry smooth-hounds were collected from fisheries surveys, fish markets and the discards of commercial trawlers. The vertebrae of these specimens were removed for ageing as shown below and the maturity and reproductive state was assessed. Once the results were analysed the findings were very surprising and showed that the Northeast Atlantic starry smooth-hound population had different characteristics to their Mediterranean relatives.
The above image shows a sectioned vertabra from a seven year old starry smooth-hound, 7 bands can clearly be seen.
Results & Management Implications
Northeast Atlantic males reach maturity at 78 cm and 4-5 years of age whilst females mature at 87 cm and 6 years of age. Males and females will also live for over 13 and 18 years, respectively. This is a significantly slower growth rate and later age-at-maturity than in the Mediterranean population, which means they are likely much more susceptible to exploitation.
Perhaps the most significant finding relates to reproduction in the females. In the Mediterranean population the pups develop for approximately 11 months before being born and females are capable of becoming pregnant again almost immediately afterwards. This is known as an annual reproductive cycle. In the Northeast Atlantic the pups develop for approximately 12 months before being born, and females then have a resting period of about 12 months before they can become pregnant again. This is known as a biennial cycle. The reasons for the variation in the reproductive cycle are unclear but they may be related to environmental factors such as water temperature and oxygen levels, which might have an effect on the speed of recovery of the females after pregnancy.
This is not the first case of this phenomenon and it has been recorded in two other species of white spotted smooth-hounds, Mustelus antarcticus in Australia and Mustelus manazo in Japan and Taiwan. Effectively those populations in colder water are half as productive as those in warmer waters, which makes them a conservation concern. This is worrying considering that Mediterranean stocks collapsed after intensive exploitation and that landings in the Northeast Atlantic are unregulated and increasing annually.
Further important information was also gathered during the project, particularly about the distribution of pregnant females and pups. Most anglers are aware of the seasonal movements of smooth-hounds, inshore in spring and back out to deeper water come autumn and winter. Temperature and prey distribution are likely to be determining factors in these movements but also the need for females to find suitable pupping grounds to give birth in. These large pregnant females are predominantly found on offshore sandbanks in the Celtic Sea and on the east side of the Irish Sea in Welsh waters. Each May these large fish appear in Holyhead Bay where local skipper Gethyn Owen of ‘My Way’ has perfected the methods for catching them.
Whilst fishing with Gethyn we tagged a number of starry smooth-hounds as part of the Inland Fisheries Ireland Marine Sport Fish Tagging Programme. Preliminary findings indicate that large females make long migrations as one mature female fish tagged off Holyhead was recaptured 257 days later over 1,100 km away by a fishing boat off Arcachon in the southern Bay of Biscay. We do not know yet why they would travel this distance, which would require a huge amount of energy, but can speculate that it is to do with the development of their pups and perhaps more favourable conditions in this area.
Unfortunately it makes what we like to consider our own fish more susceptible to the French inshore fishing fleet which operates across this region.
The project was completed in 2010 and all the results are now published in scientific journals so it is hoped that they will be used to develop some conservation measures for this species.
In summary it has been shown that Northeast Atlantic starry smooth-hounds are twice as slow growing as their Mediterranean counterparts and females produce pups twice as slowly. Therefore the Northeast Atlantic population of starry smooth-hounds are much less resilient to exploitation than the Mediterranean population and are unlikely to be able to sustain such fishing pressure. Unfortunately starry smooth-hounds have been largely overlooked and there are currently no official management or conservation measures in place to protect them. Anglers can play their part though by practicing ‘catch and release’ and handling the fish carefully.
The main thing is to support the body at all times with a hand under the abdomen. Never suspend the smooth-hound by the tail as this damages the spine and the smooth-hound will probably die after is it returned to the water even if it appears to swim off strongly. When returning the fish to the water let it rest for a couple of minutes with its mouth pointing into the current so that it can re-oxygenate it blood. These simple steps can ensure that anglers are helping with conservation whilst still enjoying the great fight that these magnificent fish deliver.
We would like to say a big thank you to Dr Farrell for his excellent series of articles.
Farrell, E.D., Mariani, S. & Clarke, M.W. 2010. Reproductive biology of the starry smooth-hound shark (Mustelus asterias): geographic variation and implications for sustainable exploitation. Journal of Fish Biology, 77: 1505-1525.
Farrell, E.D., Mariani, S. & Clarke, M.W. 2010. Age and growth estimates for the starry smoothhound, (Mustelus asterias) in the Northeast Atlantic Ocean. ICES Journal of Marine Science, 67: 931-939.
Farrell, E.D., Clarke, M.W. & Mariani, S. 2009. A simple genetic identification method for Northeast Atlantic smoothhound sharks (Mustelus spp.). ICES Journal of Marine Science, 66:561-565.
Farrell, E.D. 2010. The life-history and population biology of the starry smooth-hound, Mustelus asterias in the Northeast Atlantic Ocean. PhD Thesis, University College Dublin, Ireland.