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Marine Fisheries Research - Fisheries independent estimates of fish populations

Using video and hydroacoustic tools to provide fisheries independent estimates of fish populations

Video lander research

Video lander leaving Depoe Bay Video lander being deployed to collect video
Video landers leaving Depoe Bay, OR and being deployed to collect video

The need to develop fisheries independent estimates of demersal fish populations in Oregon remains a top priority for the Marine Resources Program. Remote underwater vehicles (i.e.. landers) have been used for this purpose in other state fisheries, and have provided stock assessment data to at least four of the regional fisheries management councils across the US.
A video lander is a remote underwater video platform equipped with stereo video cameras that allow us to observe, count, and measure fish in the ocean. Our team has designed and worked with stereo video landers with the goal of using them to conduct fisheries-independent surveys of Oregon’s demersal Rockfish communities. Our current system employs a pair of stereo cameras that allow us to measure fish length from underwater video.

Our current work is focused on determining the feasibility of using the lander tool at night. Currently, it is unknown if the species and number of fish detected differ significantly between day and night; if we find a significant difference in the abundance or composition of fish when comparing these two time periods, then researchers will need to consider these ecological differences when collecting data for stock assessment purposes.

To investigate differences in fish populations, we use the video lander to collect data on the abundance and composition of fish during day and night at four sites along the Oregon coast: two nearshore reefs (Seal Rock and Siletz), a midshelf site (Stonewall bank) and shelf break site (Daisy Bank). After collecting these data, we count and measure the fish using specialized video software and analyze the results to detect any differences. This work is currently in progress.


Combined Video and Hydroacoustic Research

In addition to the use of video landers, our team is developing a nearshore fishery-independent survey to improve stock assessments and promote sustainable management of nearshore semi-pelagic Rockfish off of Oregon. The specific goal of this survey project is to gather detailed data that will inform the selection of the optimal combination of visual survey tools and hydroacoustic data collection for quantifying nearshore rocky reef fish abundance and biomass. Specifically, we will focus on the semi-pelagic Rockfish species that are most critical to Oregon’s coastal communities.

video analysis video analysis
Image of video analysis where fish seen in the drop camera are counted and measured using a specialized video analysis tool, and an acoustic readout in Echoview program. Colored lines represent strength of signal feedback. The seafloor can be seen in red and green, while fish schools typically appear as blue blobs just above the bottom.

Determining the total abundance of nearshore Rockfish species populations would be extremely helpful in developing more reliable stock assessments, which historically struggle with scaling the population size of Rockfish appropriately. Our work was supported by a Saltonstall-Kennedy Grant to ODFW. There are two specific objectives for this project:

Objective 1: Assess the effectiveness of paired acoustic and pelagic drop-camera surveys for documenting semi-pelagic Rockfish density and biomass.

A primary challenge for an acoustic-based rocky reef survey is identifying the species composition and size distribution of schools, as species identification of acoustic targets is currently not possible for mixed schools of morphologically-similar Rockfish species. Identifying an efficient strategy for quantifying these variables using a suspended pelagic stereo drop-camera is a core goal of the proposed work. Acquiring drop-camera footage from as many different schools as possible, containing a diversity of species compositions and size distributions, will provide information on the range of school structures and allow for evaluation of the level of sampling effort that would be needed for future broad-scale surveys. Therefore for Objective 1, the focus is to conduct acoustic surveys of as many schools of fish as possible in nearshore waters (less than 60 m) over subjectively selected reef features. We plan to conduct this survey strategically along the entire Oregon coast.

In 2018, a number of single day cruises were conducted at different reefs to assess the validity of combining our suspended camera system with the acoustic data to generate population estimates. Preliminary analyses suggest this combination of tools is ideally suited for this project.

Objective 2: Assess the importance of near-bottom fish (including target species and non-target species) for interpretation of acoustic-based abundance estimates.

ROV on left with the pelagic drop camera system (i.e. BASSCAM) on right.

Evaluate the ability of three visual survey tools (drop-camera, lander, ROV) to quantify the contribution of these fish to total abundance for target species.

While the pelagic drop-camera has been developed specifically for use with the acoustic system, there is the potential for bias in its sampling frame, as it targets mid-water column data collection. Therefore it may underestimate abundance, and bias species compositions by not sampling near-bottom species that are seen in the acoustic data. Additionally, an inherent feature of acoustic data collected in high relief habitat is the presence of a near-bottom blind-spot known as the “dead zone”. ODFW Marine Resources Program has a Remotely Operated Vehicle (ROV) that is capable of capturing species composition and length distributions of benthic fish, including those adjacent to or within the acoustic dead zone. By evaluating each of these tools, in concert with the acoustic and pelagic drop-camera combination, a more complete picture of the species present can be provided and would quantify the importance of regularly sampling the benthos during a nearshore survey. To evaluate this objective, multiple reefs (Bandon, Redfish Rocks, Arago, and Orford reefs) were surveyed with all four sampling tools. Densities of near-bottom fish were compared from all three tools or tool combinations, and population estimates for each sampling area were produced. This work has recently concluded and the data is currently being analyzed.

Video and Hydroacoustic Publications and Information Reports


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