Know ledge of fish ecology and its application to habitat management Colin D. Levings 1 Levings, CD., 2004: Knowledge offish ecology and its application to habitat management; in Fraser River Delta, British Columbia: Issues of an Urban Estuary, (ed.) B.J. Groulx, D. C Mosher, J.L. Luternauer, and D.E. Bilderback; Geological Survey of Canada, Bulletin 567, p.213-236. Abstract: Information on fish habitat in th-e lower Fraser River and estuary downstream from Agassiz is presented with emphasis on geophysical factors that may be affecting fish ecology. The application to fisheries management is considered. The lower Fraser River and estuary provides habitat to support over 50 species of fish. Brief synopses are given of the ecology of commercially and ecologically significant fish. Fish communities in Boundary Bay and on Roberts Bank tend to be dominated by species adapted to marine conditions. Some brackish-water species are found in the salt wedge and on Sturgeon Bank. Our knowledge of fish ecology in the lower Fraser River and estuary is based on a patchwork of studies. To enable good management of this world-class estuary into the twenty-first century, it is prudent for stakeholders to foster ongoing programs of integrated fisheries ecosystem research in this area. Resume: eet article presente I' information disponible sur I' habitat du poisson dans Ie bas Fraser et son estuaire en aval d' Agassiz, en soulignant les facteurs geophysiques susceptibles d' influer sur I' ecologie du poisson. On y examine aussi les applications possibles pour la gestion des peches. Le bas Fraser et son estuaire servent d'habitat a plus de 50 especes de poissons; cet article presente un bref synopsis de i'ecologie des poissons ayant une importance commerciale ou ecologique. Les communautes de poisson des regions de la baie Boundary et du banc Roberts ont tendance aetre dominees par des especes adaptees aux conditions marines. On trouve certaines especes d'eau saumatre dans Ie coin sale et dans la region du banc Sturgeon. Notre connaissance de i' ecologie du poisson dans Ie bas Fraser et son estuaire est fondee sur un ensemble d'etudes disparates. Afin d'assurer une bonne gestion de cet estuaire d'importance mondiale au XXIe siecle, il serait prudent pour les interesses de favoriser des programmes permanents de recherche integree sur i'ecologie des peches dans la region. I Department of Fisheries and Oceans, Science Branch, West Vancouver Laboratory, 4160 Marine Drive, West Vancouver, British Columbia V7V 1N6 213 GSC Bulletin 567 INTRODUCTION and a comparison of the fish community in several tributaries (Alouette, Salmon, and Chilliwack rivers) (Hartman, 1968). This paper provides an overview of information on fish habitat The scope of this review is limited to species that are thought in the lower Fraser River and estuary, downstream from Agassiz, to be ecologically or commercially significant. It should be with emphasis on geophysical factors that may be affecting recognized that this is a somewhat biased approach because fish distribution. The knowledge and data are placed in the detailed biological data are not available for the majority of context of their application to fish habitat management. The fish species present in the study area. Because of concerns for lower Fraser River and estuary provide critical habitats for biodiversity (Harding and McCullum, 1994), it is likely that numerous commercially and ecologically significant fish species not mentioned in detail in this paper also are impor­ species. The influence of habitat on fish production is well tant. For example, McPhail and Carveth (1993) listed 4S spe­ recognized by ecologists. Consequently, agencies such as cies of freshwater or anadromous (fish that spawn in fresh Fisheries and Oceans Canada, which are mandated to manage water, migrate to sea as juveniles, and then return to the river fish habitat, have conducted, sponsored, or otherwise sup­ as adults) fish from the Fraser River and tributaries below the ported projects to increase our knowledge of the estuary. Fraser Canyon, of which ten were described as introduced Applied ecological science is needed to determine the func­ and four were known from single specimens only. Gordon tional relationships between physical structures, estuarine and Levings (1984) found S2 species of marine fish from and fluvial processes, and fish production. These relation­ western Roberts Bank; this is likely a minimum number ships are needed to measure the importance of various habitat because smaller individuals of noncommercial fish such as types. Management schemes, such as the Fraser River cottids were not thoroughly identified in these surveys. Estuary Management Program, were established on the Unfortunately, lack of base data and detailed knowledge of basis of such ecological knowledge and continue to rely on Pacific estuaries in general (Levings, 1994a) make it is diffi­ new scientific information to set policy. cult for ecologists to pass judgment on the biodiversity of the fish communities. Many of the commercially significant fish species found in the lower Fraser River and estuary use multiple habitats to complete their life cycle, making definition of species­ GENERAL PHYSICAL AND BIOLOGICAL specific critical habitats exceedingly complex. For example, FACTORS INFLUENCING FISH ECOLOGY IN salmon (Oncorhynchus spp.) spawn in freshwater and com­ plete a large portion of their life cycle in the northeast Pacific THE LOWER FRASER RIVER AND ESTUARY Ocean; however, the time spent rearing (growth in nursery habitat) in either fresh water (steelbead trout, O. mykiss, up to Fish ecology in estuaties and lat'ge rivers is strongly controlled S years; pink salmon, O. gorbuscha, a few days) or the estuary by the interaction of depth, tides, temperature, sediment type, (chinook salmon, O. tshawytscha, up to three months) varies and fluctuations in river discharge. In addition, biological fac­ considerably within and between species. The interrelations tors such as predation (e.g. Tompkins and Levings, 1991) and between survival in fresh water, estuary, and ocean are poorly food-web structure (Power, 1990) have likely influenced the understood (Bradford and Levings, 1997). In several adaptive features of individual species. Behavioural interac­ instances even basic biological information, such as spawn­ tions and competition between different species, such as chi­ ing locations, is unknown for the noncommercial, but numer­ nook salmon and stickleback (Gasterosteus aculeatus) ically dominant fish (e.g. minnows, family Cyprinidae). In (Sambrook, 1991), also may be an influence shaping fish comparison to other major estuaries on the west coast of communities. In the intertidal zone, the floodplain, and shal­ North Amelica such as the Sacramento-San Joaquin estuary low subtidal regions, water levels and depths determine (Conomos, 1979; Interagency Ecological Program for the whether or not particular habitats are accessible by fish. For Sacramento-San Joaquin Estuary, 1997), detailed ecological these reasons, depth and height over chart datum or lowest information from the Fraser River estuary is very limited. normal water level have been used as primary factors to describe fish habitats - low, middle, and high intertidal Fish habitats considered in this review extend from Agassiz, zones which divide the beach into biophysical units. In the approximately 11 S km from the mouth of the Fraser River, to north arm of the estuary and other channels in the estuary and the Strait of Georgia (Fig. 1), and include major tidal tributar­ lower river, these zones correspond to the biological zonation ies that enter the river in these reaches, as well as Sturgeon described in Levings et al. (1991) (Fig. 2). and Roberts banks. Because many of the smaller tributaries drain the floodplain of the lower river, these habitats also are The difference between water depth at extreme low tide mentioned. Northcote (1974) provided the first summary of and high tide, or tidal range, decreases as one moves upstream knowledge of fish ecology in the estuary and lower river. in the river. At the mouth of the river, the tidal range is about Some aspects of estuarine ecology were included in papers S m; it decreases to a few centimetres at Chilliwack during which dealt with the entire Fraser River watershed such as low river runoff. River discharge becomes a major control­ Northcote and Larkin (1989). There also have be~n a few ling factor for water levels at upstream reaches and in tribu­ papers that give summary details about the fish ecology of taries. On the main stem of the Fraser River, however, habitat particular sectors of the estuary and lower river such as outer water depth on the river margins can be described relative to Burrard Inlet (Levings, 1973; Macdonald and Chang, 1993), chart datum provided on hydrographic charts. The landward Sturgeon and Roberts banks (Gordon and Levings, 1984), boundary offish habitat on the floodplain of the Fraser River tidal marsh habitat near Ladner (Levy and Northcote, 1982), is poorly described because the extent of flooding during 214 ~o 122°39'W @ ~ I I I ~ 10 20 km '?P o 1 - Agassiz 10 - Duck-Barber-Woodward 19 - New Westminster 27 - South arm 2 - Alouette River island complex 20 - North arm 28 - Stave River 3 - Barnston Island 11 - Fraser Canyon 21 - Pitt Lake 29 - Steveston 4 - British Columbia Ferry 12 - Harrison Lake 22 - Point Roberts 30 - Strait of Georgia Corporation 13 - Harrison River 23 - Queens Reach 31 - Sturgeon Bank Tsawwassen terminals 14 - Hatzic Lake 24 - Roberts Bank 32 - Location of former 5 - Burrard Inlet 15 - Herrling Island 25 - Salmon River 'Sumas Lake' 6 - 'Canoe Pass' 16 - Hope (at Langley) 33 - Sumas Mountain 7 - Chehalis River 17 - lona Island 26 - Sand island (at 34 - 'Surrey Bend' 8 - Chilliwack River 18 - Mission Steveston Bend) 35 - Weaver Creek 9 - Deas Slough 36 - Point Grey 37 - Westham Island Figure 1. Map ofth e study area showing the locations andfish habitats mentioned in the text.