CM 1988/M1~ the Exploration of the Sea Anadromous & Catadromous Fish Committee

. •

International Council for CM 1988/M1~ the Exploration of the Sea Anadromous & Catadromous Fish Committee

FLUCTUATIONS IN THECOUNT, CATCHES AND CHARACTERISTICS OF IRISH SALMON FROM SELECTED RIVERINE FISHERIES

by Eileen Twomey r Fisheries Research Centre Abbotstown Castleknock • Dublin 15

ABSTRACT

~luctuations in the catches of Irish salmon have been weIl documented over the years by Irish salmon workers. Catch statistics relating to two estuarine fisheries are discussed to show the changes that have occurred both in the numbers and characteristics of salmon being exploited in the inshore draft (seine) net and traps from 1948 to 1987. Up to the late sixties the salmon catch in thc inshore nets and traps ware subje~t to tha normal fluctuations that occur in salmon catche~. With a change in thc regulations governing drift netting there was a marked decline in the numbers of salmon taken in the inshore nets and traps. This 1s also reflected in the count of salmon entering the River Shannon. A corresponding increase was notcd in the numbers of fish taken in the coastal drift net fishery. This change in the pattern of exploitation was confined to the 1 soa winter fish. The coastal drift net fishery takes place in thc summer months June/JulYi whenthe bulkof the 1 sea winter fish make their appcarancc in Irish coastal waters. This change in pattern of exploitation is also reflected in the reported catch statistics for the whole country. In 1960 19% of the catch was taken in drift nets. This increased to 85% in 1985.

-1- / \

1. Introduction: .,... This paper describes the 'fluctuations iri the annual catch of salmon from two river systems. Also thc numbcrs of· fish counted through Thomorid Weir on the River Shannon which gives the total count of all salmon entering this system. This data is plotted against thc nufubers of salmon taken in the drift net fishcries extending from the Donegal coast in~the north west to the Kerry coast in the south west of the country Fig. 1 shows thc location of thc rivers and the drift net fisheries described in this paper. 2. Material & Method: Annual catch data is available from the RiverMoy from 1948 to 1987 and the River Corrib for 1956 to 1985. The total count of • fish is available in a daily basis for the River Shannon from 1941 to 1982. The catch data and count is expresscd in 5 year moving averages. Based on time of ,running and scale analysis the catches for thc River Moy and River Corrib and thc count of fish at Thomond Weir on the River Shannon is classified either as 1 sea winter or multi sea winter. The drift net fishery takes place in June!July; Scale analysis has shown that 98 per cent of the fish. taken in this fishery ar'e 1 'sea winter ftsh.·

3. Results: . \. 3.1 River Moy. River catch data for the River Moy is expressed graphically in Fig. 2 as 1 sea winter and multi sea winter (mostly 2 sea winter) fish. The data was obtained from the Moy Fishery Company who operated the fishery until it was purchased by the State in 1987. The classification into 1 sea winter and 2 sea winter is based on the analysis of the stock • carried out from 1954 to 1956 Twomey (1956) and from 1967 to 1969, Wcnt and .Twomcy (1971). The average annual catch of 1 sea winter fish was high in the period 1953 to 1964. There was a dccline in the catch of 1 sea winter fish from 1965 to 1967 with a slight increase from 1968 to 1973. From 1974 onwards thcrc is a marken decrease which continued through to 1987. In Fig. 3 the Moy 1 sea . winter ,fish are plotted agairist the catch in ~he Donegal and North Mayo (North West drift nets). The decline in catch in the River Moy from 1965 onwards can be associated with the increased numbers of fish taken in the drift nets. It is known that the Donegal and North Mayo drifts exploit a proportion of the 1 sea winter stocks which are destined for the River Moy, Went (1958) Moriarty (1968).

-2- , . r"•• ,. ~\~ ..- .

, .

The earlier run fish (February/May) are not exploited by the 'drift nets. There is, however, a decline from 1975 on~ard, in the 2 sea winter component also.

3.2 River Corrib: The Galway Fishery is'the term given to the .commercial fishery in "the River Corrib. Up:to 1982 the fishery was in private hands. In 1983 it was acquired by the State. Catches of 1 sea winter and multi sea winter fish for the period 1958 to 1985 are given graphically in Fig. 4. In the case of the Galway Fishery fluctuations in catches could be in part due to change in effort. Up to the mid sixties both nets and traps were operated. Thereafter nets were operated spasmodically and since 1972 are no longer in use~ .~. • The catch in this fishery has been divided into 1 sea winter and multi sea winter fish on the basis of scale analysis and time of run. Hewetson (1958) and Browne (unpublished data). There was an increase in the numbers of 1 sea winter fish during the period 1963 to 1975 and a similar increase was in evidence in the multi sea winter fish from 1964 to 1971:' There was a marked decline in the catch of 1 sea winter thereafter up to the present time. The decline in multi sea ~inter fish occurred from 1980 onwards but is not as marked--as the 1 sea winter fish. The decline in catches of the 1 sea winter fish from 1971 onwards can be associated with the commencement of a drift net fishery in 1969. Prior to this drift netting was prohibited in the Galway area. Adult tagging of salmon in the drift net fishery, McCarthy (1987) and microtagging of smolts in the River Corrib Browne (1988) has shown that the Corrib contributes a substantial amount of fish to the Galway and North West drift net fishery. In Fig. 5 the 1 sea winter fish are plotted against the catch in the Galway drift net fishery and the decline can be associated with the increase in catch in the Galway drift net fishery. 3.3 River Shannon: An important fishery in the Shannon was that of Thomond Weir at which the daily runs of salmon were recorded fram 1941 to 1982. A total count of salmon entering the system was available from 1941 onwards. The Thomond Weir Fishery ceased operation in 1978 but the count of salmon continued until 1982.

-3- , ": ,~,:' .. .. '- .... ' ......

Scale analysis was carried out, over'a 'lo~g period -from sampIes taken at the commercial fishery in Thomond lveir; Went & Twomey (1971). Based on scale analysis and time of run the cqunt of salmon has been characterised into 1 sea winter arid multi sea winter (mostly 2 sea winter). The total count together with the 1 se~,,~inter and multi sea winter components ~s given in Fig. 6. The level of 1 sea winte~ fish in the River Shannon was high in 1941 hut it declined f~om 1945 to 1948. Thereafter the stocks showed an increase and this was reflected hoth in the 1 sea winter and 2 sea winter fish. There was a further increase in the 1 sea winter component from 1965 to 1971 but a 'decline was in evidence from 1972 onwards. There was a corresponding decline in the 2 sea winter fish during the same period but it was not as marked as in the 1 sea winter fish. 41 As in the case of the River Moy and the River Corrib the commencement of the drift net fishery along the Galway and Kerry coast was an important factor in reducing the numbers of fish entering the River Shannon~ Fig. 7 shows the dramatic risein the drift net catches in the Kerry area and the increase 'also in the Galway area. The decline in the stocks of 1 sea winter entering the Shannonis associated with the commencement of the drift net fishery in 1969. The microtagging.programme of smolts which was initiated iri the R. Shannon in 1979 has shown that the Shannon fish are heavily e~:ploited hy these drift nets, Browne (unpublished data 1979-1987).

3~4 Nominal catch statistics: Catch statistics have been compiled annually since 1945. For the purpose of this paper the proportion of fish byweight taken by instruments of capture are given in Table 1 for the period 1960 to 1986~ The main instruments of capture are the • coastal drift nets and the inshore draft nets. The revokation of the ban on drift netting in 1969 resulted in an increase in 'the driftnet catch with a correspondence decrease in the catch taken by the inshore draft nets. In 1961 the proportion of fish taken in the drift nets was 16 per cent. By 1985 it had increased to 85 per cent Anon (1987).

4. Discussion: Except for the River Shannon the information given in this paper has been obtained from the catches and not from the runs of fish. The information available suffers from this defect but in the absence of other data it must be used to assess the nature of the fluctuations iri the salmon stocks.

~4- ' ..------

.,"

The weather has an important bearing on the degree of ~'exploitation rit any one time~ The traps in the River Moy and the River Corrib.are not efficient during periods of·high 'water~ The draft (seine) net on the other hand cannot operate effectively in times of heavy flood partly because the gea~ itself becomes inefficient and partly because the fish tend to run through.the estuary quickly irito freshwater, whereas in ~drought conditions fish do not enter freshwater easily and are ~~subj ect to capture as they move up and down the estuary with 'the tide. Efficiency of drift nets is also affected by weather conditions •" In the case of both the River Moy and River Corrib catch statistics ~re reasonably accurate and it may.be possible in the future to associate it with.effort since both of these fisheries are being managed by the state. The effort in the drift net fishery has changed over the ~ears. Catch statistics are available for the Doriegal and North Mayo fishery from 1925 to the present daY. The number and size of boats fishing and the gear used bears no comparison with the ea~lie~ years. Up to 1973 the North West drift net fishery had nO,apparent effect on the catches of salmon in the River Moy. As the average catches in th~;estuary were reasonably . high despite high c~tches in the drift nets, but the escalation of drift netting in this area in the mid seventies resulted in a decline in the catches of 1 sea winter fish in the Mo~. The decline in the catches of 1 sea winter fish in the Galway Fishery can be associated with the revokation of the regulations prohibiting drift netting in 1969. The decline began in 1972 and it reached an all time low in 1979 and.1981.· From 1982 oriwards there was a marginal increase which could be associated with a stabilisation of the catch in the drift. nets. The.catches in the Galway drift net fishery did not increase at the same rate as the ether drift net fisheries along the coast. The River Shannon is the only river in the country where a total count is available over a long period (1941-82). The count of fish .entering the river has been subject' to the normal fluctuations which may be associated with marine mortality. But a decline in the stocks was evident from 1972 onwards and this "Jas more in evidence in the 1 sea winter than in.themulti seawinter component. This decline is associated primarily with the Kerry drift net"fishery where the catch escalated from a mere 1 000 fish in 1971 to 44 000 in 1984.

-5- Catch statistics.for sal~on'have been:compiled'annually since 1945. Separate statistics are available from both drift and draft·nets for the period. Up to 1969 coastal drift netting was confined to the North West coast. With the revokation of the regulations prohibiting drift netting"and a grant-iri-aid scheme for the purchase of larger boats the' catches by drift nets escalated at the expense of the inshore nets. No information is available on the effects the increased exploi~ation has on Irish salmon stocks with the exception of two river systems, the Burrishoole system and the River Shannon, where a decline on escapement into freshwater has been recorded. REFERENCES Anon, 1987. Report of the Salmon Review Group, Stationery Office, Dublin .- Browne, J. 1987. The use of Leslie Matrices to assess the salmon population of the Corrib in Atlantic Salmon planning for the future. London Croom Helm.

Browne, J. unpublished data 1979-19~7. , i . . Hewetson, Anne 1958. Salmon of the;River Corrib in 1956,1957 and 1958. Sea & Inland Fisheries Report 1958. McCarthy, D.T. 1980. Salmon movements in Galway Bay in 1978 and 1979. Fishery Leaflet No. 104, Department of Fisheries and Forestry, Trade &.Information Section, Dublin Moriarty, C. 1968. Movements of salmon around Ireland. From the North Mayo coast (1962-1964) Proc. R. Ir. Acad. 66B (1) 1-7~ went, A.E.J. 1958. Salmon movements around Ireland VIII. From drift nets along the coast of County Donegal (1953-1957) Proc.R. Ir.Acad. 58B (10) 205-212. Went, A.E.J. & TwomeYi Eileen 1971. Fluctuations in the characteristics in Irish salmon Irish fish Invest. Series A (freshwater) No. 7. Stationery" Office, Dublin. Twomey, Eileen 1956. Salmon of the River Moy Sea & Inland fisheries Report for 1956. Stationery office, Dublin.

-6- Table 1: Percentage of Salmon catch by various instruments of capture (1960-86)

Year Drift Draft Other ' ... Nets Nets Methods % % %

1960 19 51 30 1961 16 55 29 1962 21 57 22 1963 24 49 27 1964 25 50 27 J965 28 44 25 1966 32 41 27 1967 37 39 24 1968 38 39 23 • 1969 49 35 16 1970 49 36 5 1971 50 36 14 1972 64 24 12 1973 66 23 11 1974 72 ... 0 8 1975 68 24 8 1976 70 20 10 1977 75 17 8 1978 71 22 7 1979 82 12 6 1980 72 19 9 1981 75 12 13 1982 76 15 9 1983 83 11 6 1984 75 16 9 1985 85 9 6 1986 84 9 7

-1- ~~ ct-~ ~-===~~

. FIG_o_1. LOCATIONS OF RIVERS :AND DRIFT NET FISHERIES Fig.2 Moy Fishery (1948-87) 30

2 sea winter 25 D 1 sea winter

20 ,/ (J) -.. 0 0 ,....0 15 :":1 -_.. -C () -+- 0 () 10

o JJ J-r-l---r----r JIJJJJ J I O~Nn~~~~romo~Nn~~~~romo~Nn~~~~romo~Nn L{) ~ L{) L{) ~ ~ ~ ~. LO ~ ~ CD CD CD CD CD CD CD CD CD ~ ~ !" ~ ~ .!" !" !" 1".. ~ OJ ro OJ ro Fie Year MovingAvera~e.

-' Fig.3 Moy Fishery/North West Drifts 250

--+-- Moy Fishery o North West Drijts 200

CI) -0 150 0 0 ...- -C. 0 -f- 0 100 Ü

-I 1 1 I 1 o ;--.,.-.,--r---r--'---~r---1---.---r---r-y--r--r--r---Ir----1I:--TI--rI·:-:-_'-1--T-:1. _.I III tl-I ...:.1.:::::c::r::: I O~Nn~~w~romo~Nn~~w~romo~Nn~~w~romo~Nn ~~~~~~~~~~wwwwwwwww~~~~~~~~~~~rororooo Fi~ Year Moving Averagi· L----'--- _ Fig.4 Galway Fishery (1954-85) 8000

--+-- 2 sea winter 6000 o 1 sea winter

..CI) o o o r- 4000 ..c o 0+-o U

2000

FiVj Year Moving Averag.

------'------Fig.5 Galway Fisnery/ Galway Drifts 25000

Galway Fishery 20000 o Galway Drijts

...CI) o 15000 o o

..c o . -0 10000 o

5000

.. 0 "I r-T-..-T,-r-r-r-.-r--r-I 1 I II romo~Nn~~m~romo~Nn~~m~romo~Nn~~ ~~wmww~mmmmm~~~~~~~~~~rororororooo Fie Year Moving AverQ~

L'_ _ L _ Fig.6. R.Shannon Salrnon 'Nurnb'€rs 20000

2 sea winter o 1 sea winter

>( Total Count 15000

CI) -0 0 0 ~ 10000 ..c 0 -+- 0 ()

5000

ive Year Moving AverCiiJe Fif!.7 S·hannon Count/Kerry/Galway Drift~ 50001r

Shannon Count '40000 o Galway Drift )( K erry Drift ./

..CI) o 30000 o o ..s:: u -0 20000 o

10000

o r-r-I I ril-r-I I)IIII )) II J IIIIII .-r I)III ~m~romo~Nn~~m~romo~Nn~~m~romo~Nn~~m~romo~Nn~~ v~~~~~~~~~~~~~~wmmmmmmwmm~~~~~~~~~~rororororo~

... t • F. Year Moving AverarJA