Visual surveys provide baseline data on small vessel traffic and waterbirds in a coastal protected area

Abstract

The coastal waters of southern British Columbia, Canada, encompass habitat of international conservation significance to coastal and marine birds, including sizeable areas designated in the early 1900s as Migratory Bird Sanctuaries (MBS) to protect overwintering waterfowl from hunting near urban centres. Two of these, Shoal Harbour (SHMBS) and Victoria Harbour (VHMBS), have seen significant marine infrastructure development in recent decades and experience considerable vessel traffic. Vessel-related stressors are known to affect waterbirds, but traffic characteristics in coastal urban areas are poorly understood for the smaller vessels not tracked by Automatic Identification Systems (AIS). We conducted a pilot study using shore-based observers to develop small-vessel baselines for the winter months, when regional waterbird numbers are highest. During our surveys we recorded considerable inter-site variability in vessel traffic characteristics, with one site (SHMBS) a source of nearly twice as many vessel transits as the other (VHMBS). Most recorded vessels were small watercraft (mean length 26 ± 17', mode 18'), and vessels at the high-traffic site were both shorter and faster on average. One in six vessels were classified as 'noisy', of interest given that noise is an important component of vessel disturbance of waterbirds and other marine animals. Few vessels (7% of all recorded) were of the type required to carry AIS transponders, which highlights the monitoring gap created by using AIS-based approaches alone in nearshore waters, and allows for correction of AIS-derived vessel counts. Waterbird community composition also varied by locality, with one site dominated by gulls (Laridae), cormorants (Phalacrocoracidae), and seaducks (Tribe Mergini), and the other by gulls, cormorants, and alcids (Alcidae). Our results demonstrate that fine-scale local variability must be taken into account when managing for vessel traffic disturbance of waterbirds, particularly at sites of high human population density and increasing coastal development.

Fig 1. Study areas (Victoria Harbour and Shoal Harbour Migratory Bird Sanctuaries, Capital Regional District (CRD), Canada) showing spatial conservation designations, viewpoints, and passage lines (see text for details).

Map generated by Alexandra King, Environment and Climate Change Canada. For the data source of Birds Canada (2022), listed in the figure, see [14].

Fig 2. Boxplot summarizing daily counts of vessels (A) and raw daily count data (B) per survey site, Ogden Point (VHMBS), and Roberts Point (SHMBS), Greater Victoria, Canada.

Fig 3. Vessel type count by survey site, Ogden Point (VHMBS) and Roberts Point (SHMBS), Greater Victoria, Canada.

Abbreviations: CN = canoe, FV = fishing vessel, KY = kayak, MV = other motor vessel, MZ = inflatable, PI = pilot vessel, ROW = rowboat, SUP = stand-up paddle board, SV = sailboat, TB = tug and barge, TU = tug, UN = unknown (heard but not seen).

Fig 4. Frequency distribution of estimated maximum vessel speeds, Ogden Point (VHMBS) and Roberts Point (SHMBS), Greater Victoria, Canada.

Fig 5. Distribution of daily vessel counts by day of week (weekend vs. weekday) and location, Ogden Point (VHMBS) and Roberts Point (SHMBS), Greater Victoria, Canada.

Fig 6. Total counts of waterbird species recorded on hourly 3-minute surveys over 12 survey days, December 2020 to February 2021, Ogden Point (VHMBS) and Roberts Point (SHMBS), Greater Victoria, Canada.

Abbreviations are standardized 4-letter alpha codes: AMWI = American Wigeon (Mareca americana); ANMU = Ancient Murrelet (Synthliboramphus antiquus); BAEA = Bald Eagle (Haliaeetus leucocephalus); BAGO = Barrow’s Goldeneye (Bucephala islandica); BLOY = Black Oystercatcher (Haematopus bachmani); BLTU = Black Turnstone (Arenaria melanocephala); BOGU = Bonaparte’s Gull (Chroicocephalus philadelphia); BRAC = Brandt’s Cormorant (Urile penicillatus); BUFF = Bufflehead (Bucephala albeola); CANG = Canada Goose (Branta canadensis); COGO = Common Goldeneye (Bucephala clangula); COLO = Common Loon (Gavia immer); COME = Common Merganser (Mergus merganser); Cormorant sp. = Cormorant species (Phalacrocoracidae); DCCO = Double-crested Cormorant (Nannopterum auritum); GBHE = Great Blue Heron (Ardea herodias); GWGU = Glaucous-winged Gull (Larus glaucescens); GWGUX = Glaucous-winged Gull hybrid; HADU = Harlequin Duck (Histrionicus histrionicus); HOGR = Horned Grebe (Podiceps auritus); HOME = Hooded Merganser (Lophodytes cucullatus); LTDU = Long-tailed Duck (Clangula hyemalis); MALL = Mallard (Anas platyrhnychos); MAMU = Marbled Murrelet (Brachyramphus marmoratus); PECO = Pelagic Cormorant (Urile pelagicus); PIGU = Pigeon Guillemot (Cepphus columba); RBME = Red-breasted Merganser (Mergus serrator); RHAU = Rhinoceros Auklet (Cerorhinca monocerata); RNGR = Red-necked Grebe (Podiceps grisegena); SBIG = Short-billed Gull (Larus brachyrhynchus); SUSC = Surf Scoter (Melanitta perspicillata); UNLG = Unidentified Larus gull; WWSC = White-winged Scoter (Melanitta deglandi).