Hakai Beach Institute’s (HBI) herring monitoring currently consists of 4 components that are meant to track herring spawning events spatially and temporally. Through a long-term monitoring program we will address questions related to interannual variability in spawn size and location, as well as the physicochemical variables and substrate choice influencing herring spawning events, development and growth of early life stages. A brief overview (below) outlines our current monitoring methodology.
1) Mapping of spawn locations
To map the total length of the shoreline where herring roe has been deposited, we conduct surveys at low tide and note the presence and absence of herring roe. We use binoculars to look for telltale sign of seaweed coated in roe from afar (white coloration, bumpy texture), and jump ashore if a close-up visual ID is warranted. These surveys do not quantify spawn events that occur in the middle of the channel or in deeper waters, but can be used to record the general shoreline extent of individual spawning events.
Map showing the 2013 spawning events in the Hakai environs: Spawns occurred in Pruth Bay (Kwakshua Channel), Kwakume Inlet (inside and outside the Inlet), and Kildidt Sound (Kittyhawk Group).
2) Dive surveys
To determine how deep, and how far from shore, the herring spawn extends, divers conduct transect from the deepest extent of spawn to the shallowest extent of spawn. The shallow sites are often located in the intertidal, so these can be conducted without diving (see photo below). Divers swim in teams up the transect line and use quadrats to sample the substrate on which the herring spawn. Quantifying herring roe consists of measurements of percent cover, and egg layer thickness on the available substrates in the quadrat. This methodology has been adapted from DFO spawn surveys, which are conducted annually. In addition, the HBI dive surveys also quantify all the fauna present in the quadrat (namely invertebrates). Using the information from the dive surveys and the mapping, the average abundance of roe can be scaled up to provide estimates of the total amount of herring roe deposited at a spawn location.
HBI Diver (dive support boat), and dive team (Dawson, Rod and Grant) sample herring spawn site the intertidal with quadrats
3) Water column factors affecting herring spawning
Using oceanographic sampling equipment, key physicochemical variables are measured that may affect the location, timing and duration of herring spawning events. These measurements are also part of standard HBI oceanographic monitoring which includes sampling of key parameters at designated stations in Kwakshua Channel (the Kwakshua Survey). CTD (conductivity, temperature, depth sensor) measurements are taken at all stations, with additional sensors to measure a host of key water column parameters including dissolved oxygen, fluorescence, and PAR (photosynthetically active radiation nutrients). Light attenuation is measured using a Secchi disc, and a Van Dorn water sampler is used to gather nutrients, chlorophyll (phytoplankton pigment), and POM (Particulate Organic Matter) at two depths (5m, 30m). During the HBI herring monitoring, the oceanographic survey is extended to encompass the entire region around Calvert Island where herring spawn events are monitoring (Herring Oceanography Survey). Throughout the month of April, the oceanographic work in Kwakshua Channel and the larger scale survey is ramped up, sampling at higher frequency to ascertain the factors at play in herring spawn events and early life history.
4) Herring egg development and early life stages
The numbers of herring eggs (roe) deposited on the shore is truly outstanding, but how many of these actually survive and make it to return to spawn as an adult? How does this change from year to year, and what factors affect herring development? To answer these questions we are monitoring herring egg development, as well as herring larvae that hatch out and become planktonic.
Herring egg development is monitored on blades of seaweed (Fucus gardneri – see photo below). At 3 day intervals post-spawn, Fucus is collected at three of the Pruth Bay spawn sites. Ten blades per site are examined under the microscope and percent cover of the different stages of embryo development are recorded. Unfertilized eggs, hatched-out eggs, and decomposing eggs are recorded. This survey provides a chronology of herring egg development, and will be repeated yearly at proximate spawn locations to HBI.
Once the herring roe have hatched out, larval sampling allows us to quantify their size, abundance, and source of food (planktonic prey). This sampling is conducted at the oceanographic stations, with concerted effort in Kwakshua Channel this year. Bongo nets are used for these plankton tows to catch both larvae, and their sources of food. Sampling for herring larvae is conducted for a month after the spawn to quantify their growth rates and distribution.
Thanks to a terrific team at HBI, and a fortuitous spawning event right in Kwakshua Channel, the inaugural year of herring monitoring was a huge success. The team included HBI oceanographers and divers: Skye McEwan, Brent Callegari, Rod Wargo, Dawson Korol, Nelson Roberts, and was overseen by Dr. Brian Hunt and Dr. Margot Hessing-Lewis. Thanks also to the amazing chefs for feeding us so well, and the rest of the awesome HBI staff. Looking forward to Herring Season 2014!