7.1.2 Basic Instructions for Harvested Kelp Measurement

7.1.2.1 Fishery reports

These reports are most commonly released by the local fisheries management agency. Report values may require 6–18 months to be released, so this information is not instantly available. Further, the reports are for larger regions, and users are often unable to attribute the benefits back to a specific kelp forest.

7.1.2.2 Beach surveys

Users may visit harvest locations and directly survey resource extraction during the harvest period. This method may be done once for a snapshot or repeatedly over the season to gain a better understanding of day-to-day or month-to-month harvest variation.

7.1.2.3 Industry surveys

Users may directly contact industry bodies and cooperate or collaborate with them to gain access to harvest records.

7.1.3 Pros and Cons for Each Measurement Option

Table 22. Pros and cons of harvested kelp measurement options.

7.2 Fish and Invertebrate Standing Stock Biomass

Fish and invertebrate standing stock biomass refers to a snapshot (standing stock) of the fish or invertebrate biomass present in an ecosystem. Standing stock biomass is reported in weight per unit area for fish and large invertebrates, and in weight per kelp individual or biomass for epifauna and small invertebrates.

7.2.1 Measurement Options for Fish and Invertebrate Standing Stock Biomass

Sampling of kelp forest biodiversity is covered in greater detail in the biodiversity section (Section 5.1) and is a requisite for the approaches described below.

Removing fish or invertebrates from a reef to determine their biomass is typically not sustainable for long-term monitoring programs. Users may capture or estimate the animal length and then use established, weight-length relationships to estimate the biomass of the fish.

Length estimates may be done in the water by snorkelers or divers. This approach is less accurate but the most time efficient. Before surveying, users should train themselves to identify known lengths underwater to better estimate the fish length. Users can use fish cutouts or simple sticks with known lengths as tools to practice assessing length.

Stereo underwater video surveys are a more time-intensive, but more accurate method for obtaining fish biomass. Simply put, the user swims an apparatus containing two synced cameras which are recording along the transect line. This video is then later loaded into specialized software (e.g., EventMeasure) allowing calculation of fish length and identity.

Users may wish to separate their monitoring into different depth sections. These may include animals found adjacent to the seafloor, animals found mid-water, and animals found on or near the surface.

New technology means that these surveys may soon be done remotely or autonomously with AUVs/ROVs running the surveys and recording the video. Further advances may also automate the identification of species and estimate their length.

7.2.2 Basic Instructions for Measuring Fish and Invertebrate Standing Stock Biomass

See Section 5.1 for full details on counting biodiversity.

Once you have the length and identity of the individuals, obtain the weight length parameters for the species you observed. These parameters are available on FishBase. You may also use an R package called rfishbase to efficiently attach parameters to your data. If data is not available for the specific species, you can use parameters from other species in the same genus or family.

Compute the weight of each individual using the equation W = a*Lb where W = weight, L = length, a and b are parameters.

Certain invertebrates may also have parameters available (e.g., Sealifebase). If they do not, common weights may be found in the literature.

7.2.3 Pros and Cons of Each Measurement Option

Each method of fish and invertebrate standing stock biomass measurement has pros and cons for implementation (Table 23).

Table 23. Pros and cons for fish and invertebrate standing stock biomass measurements options.

7.3 Fish and Invertebrate Biomass Production

The annual rate of biomass production in fish and invertebrates is reported in weight per unit area per unit time.

7.3.1 Basic Instructions to Measure Fish and Invertebrate Biomass Production

Measuring the secondary production of a fish or invertebrate is a complex process that may be too expensive for most projects.

Rather, projects can use established relationships between an organism’s standing stock biomass (i.e., weight) and its biomass production. These relationships are available at a coarse level for all organisms (e.g., fish versus invertebrates) and may be available at a higher resolution for select species.

It is possible to calculate productivity of fish and invertebrates by collecting project-specific data, but it is resource-intensive. All methods, however, require catching, tagging, weighing, and releasing individual fish, and repeating the process at a later date. As a result, very few, if any, projects have the resources to undertake such monitoring at ecologically meaningful scales.

See the basic instructions for measuring fish standing stock biomass in Section 7.2.2. Generally, the steps are to:

1. Obtain fish biomass per m2.

2. Transform the biomass values into production values using biomass to production ratio values ¹.

7.3.2 Pros and Cons for Each Measurement Option

Each method of annual biomass production measurement has pros and cons for implementation (Table 24).

Table 24. Pros and cons of annual biomass production measurement options.