(1) Female wading birds arrive at the head of the Bay of Fundy in early to mid-July carrying a moderate parasite load. Over the three weeks they spend there, the parasite load drops as they feed on Corophium, doubling their weight before starting the long (3,000 miles), non-stop haul to South America where they overwinter. As they are leaving the mudflats, the males and juveniles are arriving also carrying moderate parasite loads. However, during the time the females were there, the Corophium (and snails and polychaetes) were becoming infected with various parasite larval stages (from the parasites the females brought in). These infective larvae are then available to the males and juveniles so that by the time they start their southern migration, they are carrying relatively heavy parasite loads with some mortality occurring en route. (The proportion of mature females arriving on the overwintering grounds is higher than that of mature males and juveniles)

The above descriptive scenario is being examined on a quantitative basis this summer. A UNB Honours student (Nicole Bourgeois) is examining the prevalence and intensity of parasites in Corophium, snails and polychaetes establishing the baseline data during June, and documenting quantitative changes in parasite burdens over the period that the mature female birds, and then the mature males and juveniles, during July and August. Helping with this project are two colleagues of mine, Dr A.S.Didyk and Dr D.G.Crowe.

(2) It is well-established in the literature that factors causing stress can be accumulated by organisms to the point that they cause death. The early work of John Sprague (then at DFO, St Andrews) established the concept of lethal

units w.r.t. heavy metals. For example 48 ppb copper would kill juvenile Atlantic salmon whereas it took 600 ppb of zinc. These constituted lethal units for these metals when present in the absence of other toxic metals. However, half of the lethal unit for copper (24 ppb) plus half of the lethal unit for zinc (300 ppb) would make up a complete lethal unit that would kill fish. Taken further, this means that 10% of the lethal units of 10 toxic metals could make up a lethal unit capable of causing mortality. There are a number of instances where it has been shown that combinations of certain metals can decrease the individual toxicities and other instances where certain combinations can exacerbate the individual toxicities. Work that I have been involved with in recent years looks at parasitism as a stress factor which, in combination with other stress factors such as heavy metals, is cumulative and can lead to death of the host organism.

As part of the Collaborative Mercury Research Network (COMERN) Centre of Excellence, a group of us have been looking at mercury levels in various organisms, at different trophic levels in the food chain, in the Bay of Fundy

coastal ecosystem (the New Brunswick side of the Bay). My interest, specifically, is to relate these levels to parasite loads and to mercury levels within the parasites themselves (as the "top" predator). Where metal levels are relatively high, we find no fish with large numbers of parasites but where metal levels are low, there is always a small proportion of fish with heavy parasite loads. This suggests that in the presence of significant metal toxicity, the fish cannot survive the extra stress caused by large numbers of parasites and such heavily parasitised fish die. In some cases, the

mercury levels in the parasites are much higher than in the fish they parasitise which could be interpreted as being beneficial to the fish by removing metals that might otherwise have been taken up by the fish. Helping me with this work is a graduate student (Chris Blanar) and two undergraduate students (Jesse Bourque and Georgina Cox).

Report to 2008 AGM

This working group is addressing the question of how to assess cumulative change in the Bay of Fundy, caused by exposure to multiple factors in different scenarios of time, space and intensity or concentration. Two studies looking at the interactions of mercury exposure and parasite burdens have been conducted to date. The current study, conducted by a masters graduate student, has the goal tof developing a new PCR based tool for detecting stress caused by parasite infections in fish.

Two parasitic pathogens pose potential problems for the cod aquaculture industry as it develops. One is a unicellular microsporidian (Loma morhua), which is already causing mortality in young caged cod in the Bay of Fundy; the other, one of several species of Gyrodactylus, is adversely affecting caged cod in Norwegian and Icelandic waters and will inevitably affect caged cod in Canadian waters, once the industry expands.

Our initial study looked at the two stressors of light and temperature and what effect they had on the growth of captive cod. Initially, we exposed fish to either total darkness or continuous light holding them at either 8˚ or 15˚ C. Although it came as no surprise that the fish maintained in total darkness grew better (gained more weight) than those in continuous light, it did surprise us to find that fish maintained at 15˚C grew better than those maintained at 8˚C, even though bottom temperatures would seldom get higher than 8˚ in their natural habitat.

We are currently developing a PCR assay for Loma morhua so that we can determine the long-term effects of infection with this parasite, using non-lethal blood sampling, under different environmental conditions of light and dark. We also hope to infect cod, experimentally, with isogenic cultures of different Gyrodactylus species and determine what effect cumulative stress factors have on their growth. To these ends, we have applied for a NSERC Strategic grant although we will start the work later this fall by establishing the isogenic cultures of Gyrodactylus spp. on naive, juvenile cod and testing the efficacy of our PCR assay for Loma morhua. (Submitted by Dr. Michael Burt, UNB Fredericton)