Sockeye Salmon Juveniles in Chatham Sound 2007 Report to Pacific Salmon Forum July 2008 By: Allen S. Gottesfeld Charmaine Carr-Harris Bart Proctor Dave Rolston Skeena Fisheries Commission Hazelton, B.C. Introduction In early 2002 the Government of British Columbia announced the end of a seven year moratorium on new salmon farm sites and the potential expansion of salmon farms to the North Coast. Several salmon farms were proposed in the vicinity of the Skeena River estuary in 2003. We undertook a series of studies of juvenile salmon use of the Skeena and Nass estuaries to help evaluate potential interactions between wild and farmed salmon. We investigated the ecology of caligid sea lice on salmon on the North Coast with field studies in 2004 through 2006. The data from these studies is available in Krkoŝek et al. 2007 and Gottesfeld et al. (in review). The 2007 field research was designed to define the distribution of sockeye salmon smolts in the Skeena and Nass estuaries. This is important because of concern about the potential spread of infectious hematopoietic necrosis virus (IHNV). IHN, the disease caused by this virus, is a serious endemic disease of wild and cultured sockeye. Atlantic salmon are particularly sensitive to this disease (Saksida 2003). Most outbreaks of IHN are restricted to eggs, alevins and fry at sockeye spawning areas, but IHNV can be transmitted in sea water as shown by lab tests (Traxler et al. 1993), and by the epidemiology of wild (Traxler et al. 1997) and cultured fish ( Traxler et al. 1998, St. Hilaire and Ribble 2002, Saksida 2003). We made trawl net collections of juvenile salmon in 2004 and 2005 that demonstrated the presence of sockeye juveniles in the Skeena and Nass estuaries. Juvenile sockeye were found in collections between late May and late June and were especially abundant in Ogden Channel (Gottesfeld et al. 2006). The significance of Ogden Channel as a migration corridor for juvenile sockeye is also shown by the relatively large catches in Browning Entrance at the outlet of Ogden Channel by the CCGS W.E. Ricker in 2000 and 2001 (Welch et al. 2003, Welch et al. 2004). 2 Juvenile sockeye migration routes and habitat use were explored in this study by examining the abundance of sockeye smolts, the timing of collections, the size of smolts and their diet, and by using microsatellite DNA analysis and mixed stock assignment techniques to shown the origin of smolts using the Skeena estuary. Methods Study Area Our study area included the estuaries of the Skeena and Nass Rivers. Trawl sites extended throughout the regions of freshwater influence, from Hogan Island at the east end of Portland Inlet in the north to the middle of Petrel Channel on the south, and from the mouth of the Skeena River westward to the eastern edge of Chatham Sound. In order to determine the change in sockeye abundance in different locations over time, we grouped catch locations into five generalized areas (Figure 1). Briefly, these areas are: PE for Port Edward, the region of the estuary immediately to the north of the mouth of the Skeena River; K for Kennedy Island which is in the midst of Arthur, Telegraph and Chismore Passages to the south of the mouth of the Skeena River; O for Ogden Channel, the distal portion of the estuary to the south; SC, the southern portion of Chatham Sound, to the west of Prince Rupert; and NC, for North Chatham Sound, the inland section of the North Coast section between Work Channel and Big Bay adjacent to the outflow of Nass river waters. Sampling and Analysis Sampling was conducted during a five-week period between May 26 and July 5, 2007. Samples were collected from sites within each generalized area at least once per week except during week 3, when severe weather conditions prevented fishing in areas SC and NC. Fishing was conducted with a surface trawl net that was modified from the OFL Atlantic salmon smolt net design of Holst and McDonald (2000). It was fished by the M.V. Pacific Coast, an 11 m ex-commercial gillnet vessel. The trawl net was 18 m 3 long, with an opening 5m wide and 4.6m deep. Trawl times varied in length from 10 to 77 minutes, depending on the abundance of the target species. Most trawl sample durations were less than 40 minutes. The fish were collected into a rigid holding box at the cod end designed for live capture and to minimize the loss of scales and ectoparasites. Samples were transferred into 5-gallon buckets and sorted by species. Temperature and salinity data were recorded at each site using a YSI-30 meter. Collections were counted and labeled onboard the Pacific Coast . Sockeye that were to be tested for IHN (n=200) were shipped fresh on ice to the Pacific Biological Station laboratory within 24 hours of the time they were caught. Most of the remaining salmonids were individually bagged and frozen for further analysis in the lab. A small number of sockeye from larger sets were selected for stomach analysis, and their stomachs excised and preserved in 7% formalin. Tissue samples for DNA analysis were taken from those sockeye not sent for IHN analysis (n= 437). DNA samples were preserved in 99% ethanol. Juvenile salmonids were weighed, measured, and examined in the laboratory for sea lice using a dissecting microscope. The motile stages of the lice were separated according to morphological characteristics outlined in Kabata 1972 and Johnson & Albright 1991a. Copepodid and chalimus stages of sea lice were mounted on permanent slides and identified to species and stages using a compound microscope. The contents of the preserved stomachs were examined using a Wild M-7 dissecting microscope. Zooplankton were counted and categorized at least to the level of order, and the relative abundance of each taxon was calculated. Plankton samples were taken at sites at the start point of each trawl site. Samples were taken using a 1 meter diameter plankton net with 150 um mesh in a vertical pull from a depth of 20 meters.. The filtrate was preserved with 10% formalin. In the laboratory, plankton samples were decanted into sieve stack of 1 mm, 500 μm, and 150 μm, and rinsed under a stream of water to remove formalin. The filtrate was rinsed with 4 ethanol and concentrated in a centrifuge. Subsamples of the concentrated zooplankton were examined with a counting slide under a compound microscope to determine the relative abundance of zooplankton taxa. The zooplankton samples were initially determined to the same level of taxonomic classification as the corresponding stomach contents. IHN Analysis Frozen whole juvenile sockeye were submitted to the fish virology laboratory at the Pacific Biological Station for IHNV analysis by tissue culture techniques using two cell lines. Analysis in the DFO fish virology laboratory has been severely delayed because of priority being given to work on the viral hemorrhagic septicemia virus (VHSV) epizootic that is spreading through the Great Lakes region. DNA Analysis Juvenile sockeye tissue samples were submitted to the Salmon Genetics Laboratory of the Pacific Biological Station. Collections for analysis were assembled from trawls in each of the six geographic areas shown in Figure 1. Samples were analyzed for polymerase chain reaction products at 15 microsatellite loci (1b, 3dre, beta1, i1, oki10, oki16, oki1a, oki1b, oki29, oki6, omy77, one8, ots103, ots2, and ots3). Individuals were assigned to source populations using mixed stock analysis techniques employing Bayesian mixture modeling (Pella and Masuda 2001, Koljonen et al., 2005). Proportions of collections were determined using the Coastwide 032107 baseline sample of 227 sockeye populations in a fashion similar to that reported by Beacham et al. (2005a, 2005b, 2005c). The reported stock compositions for actual fishery samples are the point estimates of each mixture analyzed, presented with variance estimates derived from 1000 bootstrap simulations. 5 Figure 1. Map of North Coast showing collection sites and defined areas. 6 Results The 2007 snowmelt flood resulted from a heavy snow pack followed by a late spring. The peak flow at Usk, the gauging station above Terrace (Figure 2.), was in the first week of June and was the highest since 1974. The peak flows in the estuary occurred about one week later and were about twice as large because they included large contributions from coastal tributary rivers. Figure 2. Discharge record at Skeena river at Usk (08EF001) for the 2007 nival flood. The large flows from the Skeena and the Nass Rivers create brackish conditions along the coast north and south of Prince Rupert. Estuarine flow is conspicuous as far as Dixon Entrance north of Haida Gwaii (Thomson 1981). Defining the estuary is difficult as the Skeena and Nass rivers debouch into a series of coastal fiords. For the purposes of this paper we define the estuary zone as the area where the freshwater component is greater then 10%. Chatham Sound and Ogden Channel, the areas discussed in this paper, had salinities with >30% freshwater component in their most marine portions during the 2007 flood (Figures 3 and 4). 7 We observed a salinity and current pattern similar to that described by Trites (1952) which first defined the circulation pattern of the Skeena estuary. Early in the sockeye juvenile residence period between late May and early June (Figure 3), the freshwater plume of the Skeena River bifurcates. One branch flows down Ogden Channel and the other turns north along Digby Island. An eddy is formed in southern Ogden Channel with marine waters flowing in through Edye Passage and along the north coast of Porcher Island. Similar flow patterns were observed in 2004 and 2005.