Lead Toxicity in Mute Swans

TABLE 1: Causes of death in Irish swans found at post-mortem. Five in the 'unknown'
category had lead shot present in their gizzards.
Location hypo- coll is- oil Tuberc- choked Unknown Total
thermia ions ulosis
Cork 2 0 4 19 33
Dublin 0 2 2 0 0 s
Clare 3 0 0 0 0 0 3
Limerick 0 0 0 0 0
Waterford 0 0 0 0 0
Mayo 0 0 0 0 0
Total 6 9 2 4 22 45
confirm acute lead poisoning as the cause of death. Chemical analyses
have yet to be carried out on the tissues of dead birds examined. Causes
of mortality in a sample of Irish swans are presented in Table 1.
Despite the lack of confirmatory chemical evidence, coarse angling
activity, both past and present, at Cork City Lough appears to be
implicated in causing the elevated blood lead levels recorded in 50% of
_mute swans sampled. At present, however, no mass mortalities have
resulted from the ingestion of discarded anglers' lead weights. Because of
the potential damage to swan populations through effects on metabolic
pathways as well as through mortalities, it is appropriate to review
angling practices in Ireland.
ANGLING PRACTI.CES AND ACTIVITIES
One of the noteworthy aspects of lead poisoning in waterfowl is its
emergence as a problem only recently. Anglers have been using lead shot
for over a century, but no mortalities were recorded prior to the 1970s. It
is now considered that a change in angling practices in the 1960s has
caused this environmental hazard. Prior to the early 1960s, anglers used
cotton lines with hooks and lead weights attached. In the early 1960s,
with an increase in fishing as a recreational activity and the construction
of many gravel pits and reservoirs, particularly in Britain, coarse and
game fishing became popular. With this change, a revolution in fishing
accessories occurred. Nylon lines were introduced and hooks and lead
weights were frequently stripped off and thrown away at the end of the
day's angling. The availability of different types of nylon lines with
different breaking strains also increased the possibility of more lead
weights being lost when lines became snagged. Thus, enhanced fishing
- 50 -
./