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Monkfish Migrations
Paddy Fitzmaurice & Peter Green
In 1970 the Inland Fisheries Trust (now the Central Fisheries Board) initiated a tagging programme for marine sport fish. At that time there was a perception that catches of sport angling species were in decline and results from angling competitions appeared to confirm this. Virtually no information existed on the migration or mobility of these species and tagging was seen as a way of gathering valuable information on their movements. The tagging programme was also effectively a conservation measure for the most important angling species, which would ensure that fish captured, were returned tagged and alive to the water rather than being killed. Sea angling tourism revenue is worth over €30 million to the Irish economy.
The tagging operation was carried out on a voluntary basis. Skippers of angling charter vessels agreed to tag the targeted species and record data on the fish in a dedicated tagging log book. Accurate details such as the tag number, location of tagging, date of tagging, length, weight and sex of the fish, were all recorded where possible so that details of the migratory pattern, if any, could be worked out from recaptures and additional information on the biology of the species could be collected.
Monkfish or Angel shark (Squatina squatina) was one of the species selected for tagging. The two prime locations for capturing numbers of these species were Tralee Bay and Clew Bay. Even in these bays, monkfish populations were known to be confined to very specific areas.
Initially two types of tags were tried out, Jumbo Rototags (which are used on the ears of cattle) and Petersen discs. The voluntary taggers found that when the monkfish were taken on board for tagging, they could be quite aggressive and great care had to be taken when they were being handled. For this reason they opted for the Jumbo Rototag which was much easier to use when inserting the tag into the dorsal fin using an applicator.
All of the monkfish tagged were caught on rod and line in shallow waters usually not exceeding 5 metres in depth. The fish was taken onto the boat, the hook was removed carefully and after details were recorded the tagged fish was returned alive to the water. The tagging programme began in 1970 and 1,107 monkfish were tagged up to the end of 2001. The captured fish ranged in size from 6.5 kg to 26 kg weight with the average size being approximately in the 14 - 18 kg bracket. The majority of the fish tagged came from Tralee Bay (939) whilst 70 monkfish were tagged at Clew Bay.
Tag Returns
The general areas of recapture are shown in Figure 1 and to-date 187 recaptures have been recorded. This represents a return rate of 18.3% which is regarded as an extremely high return rate for any tagged fish. The main bulk of recaptures have been taken by rod and line angling (47.6%), trawling (19.25%), tangle nets (16%) and gill nets accounted for 5%. 5 tags have been found washed ashore on beaches. Overall, it appears that tag retention is good. However, in situations where tangle nets are used and where monkfish are captured it is possible that tags could be ripped from the dorsal fin and because the tags are close to neutral buoyancy they could be carried ashore by water currents. All the fish recaptured by anglers on rod and line were subsequently returned to the water alive with the tag in place after their details were recorded.
179 of the returns were taken in Irish coastal waters whilst 8 recaptures were returned from abroad having been taken by commercial means. Of these, 5 were recaptured in French coastal waters, 2 were taken off the south coast of England and 1 was taken off the north coast of Spain. A movement pattern spreading north and south from Tralee Bay has been identified whilst movements from Clew Bay, to-date, show a southerly migration.
The longest number of days a monkfish was at liberty was 4,352 days (almost 12 years). This fish which was originally tagged in Tralee Bay, was recaptured 3 km north of Kerry Head after 4,325 days, released again and after a further 27 days was recaptured again off Bunmahon, Co. Waterford - some 345 km away. At least 3 further fish were at liberty for over ten years. These 3 fish were originally tagged in Tralee Bay and were recaptured within the general Tralee Bay area. The longest distance travelled by a recaptured monkfish was 1,160 km. This fish was tagged in Tralee Bay and recaptured by a trawler off San Sebastian, Spain in the Bay of Biscay. From the recapture records, it is evident that the species is long lived. This, in conjunction with the high recapture rate, demonstrates that monkfish are vulnerable to fishing effort.
In total 96 recaptures have been recorded from the Tralee Bay area which
probably reflects the localised distribution of the species. It also reflects,
to a great extent, the intensity of fishing effort by both anglers and
commercial fishing. Commercial fishing effort is not specifically targeted
at the species and any monkfish being caught would appear to be accidental.
Having analysed the angling fishing effort in Tralee Bay from 1977 onwards
there is a dramatic fall off in the numbers of monkfish being caught recently
(Fig. 2). In the five year period 1987-91, 320 fish were tagged whereas
in the period 1997-2001 only 16 fish have been tagged despite the angling
effort being relatively constant.
This long-term study has contributed to knowledge of Irish monkfish populations
but has also highlighted many gaps in our understanding of their biology.
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