Written by guest contributor Mary Beth Loewen; Edited by Patrick Cooney
In Alaska, salmon are king. As an organism and a resource, they are the pinnacle of cultural, financial, and ecological value.
To maintain salmon populations for the future, while continuing sustainable commercial harvest from Alaskan bays and rivers, it is critical that salmon populations are well understood, documented, and monitored. Considering the remote and hostile nature of Alaskan wilderness, it is often necessary that Alaskan fisheries scientists get creative to accomplish this task. Or as they like to say, they have to go ninja on the fish.
In recent years, commercial anglers and scientists throughout Alaska documented reduced numbers of Chinook salmon Oncorhynchus tshawytscha. This caused widespread concern and increased interest in determining the causal factors for the decline. Fisheries scientists from the Alaska Department of Fish and Game’s (ADFG) Westward Region, that stretches from Kodiak Island along the Alaska Peninsula to Unimak Island, have been working diligently to determine the factors contributing to the decline by getting into the field to directly monitor fish.
Many of the salmon populations on the Alaska Peninsula occur in remote streams that are generally small in size and difficult to access. While these minimally disturbed streams make for incredible salmon habitat, the lack of road or foot access precluded scientists from easily monitoring salmon populations.
ADFG scientists hired a helicopter and stealthily swooped in to observe and capture salmon…like ninjas! The scientists spent three seasons flying aerial surveys to assess and characterize Chinook salmon populations across ADFG’s Western Region.
Beyond visually observing salmon in the stream systems along the Alaska Peninsula from a helicopter, scientists also captured wild salmon to take genetic samples. This is of particular importance because previous analysis of genetic samples from the northern Alaska Peninsula indicated that Chinook salmon from this region were 1) genetically distinct from other regions and 2) have a high degree of genetic diversity among populations within the northern Alaska Peninsula.
If salmon populations are to be properly managed, it is critical that individual populations are identified and managed accordingly. The tool selected to examine the potential impacts of commercial fisheries on Chinook salmon populations was mixed-stock analysis using genetic data (MSA). An essential component of MSA is a comprehensive genetic baseline. In other words, scientists need to have genetic material from salmon runs across the region. While the Western Region of Alaska had plenty of visual observations of salmon prior to this study, they did not have strong representation in the genetic baseline, especially systems on the northern side of the Alaska Peninsula that flow into Bristol Bay.
Tools of the Trade
Tools of the trade typically used by fisheries scientists in other regions of the world to capture fish were not going to cut it in these streams for these fish. Chinook salmon run in deep and fast water, requiring enhanced gear designs. Accordingly, scientist Mark Witteveen designed and built a custom beach seine in 2012 specifically for collecting Chinook salmon in ADFG’s Westward Region. The net was 75’ long and 10’ deep, shorter and deeper than most sample collection beach seines. It consisted of 3 -1/2” stretched measure spectra web to minimize drag in the fast moving water. Additionally, the net was built with 2 pound per fathom leadline, supplemented by external lead weights on both ends to keep the leadline on the substrate in fast currents. The leadline also had purse rings attached every 3’ of length and a full length purse line all designed to reduce Chinook salmon escaping under the net. This net is heavy and robust.
After spotting schools of salmon from the helicopter, scientists swiftly dropped out of the sky and deployed their gear. The beach seine was used to encircle schools of Chinook salmon or was held in a hook pattern and schools of fish were herded into the net from the deep and fast moving water. Once the fish were encircled, the bottom of the net was pursed up to the beach and fish were processed.
In total, 2,036 Chinook salmon were sampled during the three years of this project, more than doubling the number of baseline genetic samples from ADFG’s Westward Region and southern Bristol Bay. In addition, nine populations that were not represented prior to 2012 and four populations that had low sample numbers are now all well represented.
With this information, Alaskan scientists intend to enable Chinook salmon to continue reigning as king over these waters for generations to come.