QUINE COMO FUNDAMENTALISTA

In spite of a significant sampling effort, little success was achieved in the scientific netting surveys conducted for shad on the two estuaries. No shad were captured in netting operations on the Slaney during the scientific survey, which took place over the period 26th May – 7th July 2003. Twenty-five separate operations took place over this time period (Figure 3.39). Various types of netting procedures were adopted included fixed and floating drift nets, draft nets and fyke nets. On the Blackwater, 16 young shad were captured in netting operations during the scientific survey, which took place over the period 29th May – 4th July 2003 across 8 days. As with the Slaney survey, various types of netting procedures were adopted included fixed and floating drift nets, draft nets and fyke nets. A total of 15 separate operations took place over this time period (Figure 3.40). All of the twaite shad taken in the Blackwater were caught by two floating drift nets on the 29th May 2003 at Brian’s Cúl on the Broads of Clashmore. This sample is considered to be of significance due to the relatively small size of the fish taken. No allis shad were taken in the scientific survey.

A total of 5 adult shad was made available to the study by commercial netsmen operating draft or drift nets. This sample consisted of 2 twaite shad, from the Slaney, and 3 allis shad – two from the Munster Blackwater and one from the Slaney. All three Slaney fish were taken in salmon draft nets in the estuary. The two twaite shad were taken near Ferrycarrig in the lower reaches and the allis at Macmine in the middle reaches. Of the two Blackwater fish, one was a more truly coastal specimen, being taken circa 3 km off the mouth of the Blackwater estuary. The second Blackwater fish was of considerable significance as it was captured on rod-and-line in the Careysville fishery near Fermoy. This fish had penetrated into freshwater a distance of 25 km upstream of the head of the tide at Cappoquin.

Figure 3.40: Map of the Munster Blackwater estuary showing netting operations for shad 2003

3.4.2 Archival material

Since 2000, the Central Fisheries Board has been compiling a database on shad material from Irish waters, based on samples of material collected by or submitted to it for examination and on material in published or grey literature form. This provides a listing of species, date and location of capture and such biological information as length, weight, sex, gonad condition, gill raker count, feeding activity. The material from the present survey was combined with archival material to examine some of the biological features of the two species of shad taken from the Slaney and Munster Blackwater. Typically, the two species can be distinguished in the field by examination of the gill rakers on the first gill arch under the opercular flap. The allis shad have a greater number of rakers than twaite shad and the allis rakers tend to be longer. Data from both species for the two catchments indicated a clear difference in numbers between the two species (Figure 3.41). The data also indicated a difference between raker counts of young twaite shad (<23 cm) and older twaite shad (>23 cm), suggesting that raker counts increase, to a certain level, as shad grow.

The length frequency distribution (Figure 3.42) indicated a degree of overlap between allis and twaite shad. The allis sample ranged from 40 cm to 52 cm, with fish in excess of 50 cm being taken in both estuaries. Two clusters of twaite shad were identified, the group of small fish (20 – 24 cm) taken in the present study in the Munster Blackwater and the larger group of fish (34 – 46 cm) taken in commercial drift – and draft nets. These different records reflect the different mesh sizes used. The length – weight data indicated a cubic relationship with a very high R2 value (Figures 3.43A & 3.43B). Similar cubic expressions and R2 values were obtained when the twaite data, only, and the combined twaite and allis data were used, suggesting that the allis growth form is similar to that of the twaite but can extend to greater body length, with associated weight increase.

Of the 7 allis shad examined, four had been feeding on shrimp and two had empty stomachs. Of the latter, both were females with gonad in an advanced state of development i.e. ovaries filling a large part of the body cavity with eggs clearly developed. The twaite shad with stomach contents had been feeding on shrimp or small crustaceans and/or fish. In the majority of cases, the fish material could not be identified. However, sand eel and sprat/herring were recorded in some cases.

Since completion of the present study, a further two shad were presented for examination by commercial netsmen on the Slaney. One of these was a partly spent female twaite shad taken in mid June. The second, on initial examination of gill rakers appeared to be an allis shad. This was a relatively small male fish, almost ripe, and was taken in mid May. This fish had a gill raker count of 78, suggesting it was a hybrid. The occurrence of such hybrids is a source of concern in regard to the conservation status of both species of shad in the Slaney.

Figure 3.41: Shad gill-raker numbers for allis and twaite shad in the Slaney and Munster Blackwater catchments 2000-2003

Figure 3.42: Length-frequency distribution for allis and twaite shad in the Slaney and Munster Blackwater catchments 2000-2003

Length frequency distribution: Slaney and Blackwater

0 1 2 3 4 5 6 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 Length (cm) No. fish Allis shad Twaite shad Shad gill-raker counts:

Slaney and Munster Blackwater

0 2 4 6 8 10 12 14 16 18 20 30 40 50 60 70 80 90 100 110 120 130

No. gill rakers

No

. fish

Twaite > 23 cm Twaite <23 cm Allis

Figures 3.43A & 3.43B: Length-weight distribution for allis and twaite shad in the Slaney and Munster Blackwater catchments 2000-2003

Shad length-weight relationship: Slaney and Blackwater y = 0.0221x2.8503 R2 = 0.9834 0 200 400 600 800 1000 1200 1400 1600 1800 2000 0 10 20 30 40 50 60 Length (cm) Weigh t (g) Twaite Allis Power (Twaite)

Shad length-weight relationship: Slaney and Blackwater y = 0.0229x2.8419 R2 = 0.981 0 200 400 600 800 1000 1200 1400 1600 1800 2000 0 10 20 30 40 50 60 Length (cm) Weigh t (g)

Plate 8:

Plate 9: