//
you're reading...

Biology

Some Like it Hot: Ocean Heat Content and Fish Migrations

Article: Luo J, Ault JS, Shay LK, Hoolihan JP, Prince ED, et al. (2015) Ocean Heat Content Reveals Secrets of Fish Migrations. PLoS ONE 10(10): e0141101. Doi: 10.1371/journal.pone.0141101

Background

Many people who fish will tell you that many species of fish prefer certain water temperatures or certain areas. One type of preferred fish area is a front, a swirling boundary between two water masses of differing temperatures or salinities, and fish seem to like it there because the front often enhances biological productivity. However, most of the limited evidence for fish inhabiting these fronts is pulled from fisheries data or ecological theory. Few methods have provided quantitative evidence to support the theory, in part because fish are hard to track.

journal.pone.0141101.g001

Figure 1: Sea surface temperature maps (top, a) show less detail than ocean heat content maps (bottom, b).

One method of tracking fish consists of tagging them with a device that measures temperature, depth, and light levels, as well as a GPS location if the fish is at the surface. The tag eventually pops off the fish and surfaces to transmit all the data it has gathered; hence the name pop-up satellite archival tag (PSAT). The reasons for measuring temperature and depth are clear enough, but why measure light levels? Based on the light measured by the tag, scientists can determine the time of sunrise and sunset, and from this calculate a rough location of the fish, even while it is underwater.

In the past, these rough locations have been refined using the temperature data recorded by the tag. If the fish nears the surface, the temperature can be compared to satellite measurements of sea surface temperature to correct the track to a more likely location. The researchers of this study noticed that sea surface temperature maps are often uniform and featureless in some areas, and may not provide the best check for improving fish tracks (Fig. 1a). Instead, they turned to ocean heat content, a measurement of the total heat contained in the upper layers of the ocean, as a way to map the fronts and eddies of the ocean in more detail (Fig. 1b) and better refine fish locations.

Methods

First, the study team followed a previously used procedure for refining the 137 light-based fish location tracks available. Starting with the sunrise/sunset times measured along a track, they applied an algorithm known as a Kalman filter to compare the measured temperature to the sea surface temperature measured from satellites. The algorithm adjusted the rough track locations to better align the tag temperature with the satellite measurement, as well as moved points that were too shallow or on land (Figure 2a). At this point, the tracks could be further refined using ocean heat content measurements.

Ocean heat content is a measurement of the heat contained in the upper layer of the ocean and is usually measured so that we can better track the pathways of hurricanes. The upper layer extends from the surface to where the ocean temperature is 26°C, which is the part of the ocean most important to hurricane formation, and therefore has been well-studied and documented (Figure 3). The heat energy contained in that upper layer is calculated, which gives an estimate of how much thermal energy is available for various processes. Since some of the fish species studied prefer cooler temperatures, the layer was sometimes expanded to lower temperatures (below 26°C), but the process remains the same.

Maps of ocean heat content were generated from an ocean model that uses a variety of near real-time information to predict ocean temperatures at all depths. These maps show more structure and variability than the satellite sea surface temperature maps.

The ocean heat content for each fish track was estimated using the temperature reading from the tag, and then another algorithm was used to further adjust the tracks to better match the ocean heat content maps (Fig. 2b).

 

Figure 2: a) The white line is the light based track for a single fish, while the red and green lines are two versions of the sea surface temperature adjusted track. b) The blue represents the ocean heat content adjusted track for the same fish.

Figure 2: a) The white line is the light based track for a single fish, while the red and green lines are two versions of the sea surface temperature adjusted track. b) The blue represents the ocean heat content adjusted track for the same fish.

Findings

Figure 3: a,b,d,e) The yellowfin tuna track shown here implies that the fish preferred to follow the edge of the large eddy (red blob) over several months (April to July). c) A plot of ocean temperature over time measured by the fishes tag. The black line is the 26 °C limit, and the arrows show the location of the eddy for a,b,d,e.

Figure 3: a,b,d,e) The yellowfin tuna track shown here implies that the fish preferred to follow the edge of the large eddy (red blob) over several months (April to July). c) A plot of ocean temperature over time measured by the fishes tag. The black line is the 26 °C limit, and the arrows show the location of the eddy for a,b,d,e.

The study found that using the more detailed ocean heat content map increased the resolution of the fish tracks. This higher level of detail revealed that most of the fish did tend to follow fronts and eddies and stay on their edges, just as ecological theory predicts (Fig. 3). When the tags were active, these frontal areas made up about 18% of the total habitat available to the fishes. Despite this small fraction, more than half the fish spent over 60% of their tracked time in a front. The authors point out that these results are sensible, since using ocean heat content (which includes temperatures at depth) rather than surface temperatures better reflects the way a fish interacts with the ocean, moving up and down through temperature layers (not just remaining near the surface).

These results, which have not been attained with any other method, show that using ocean heat content to refine the fish tracks greatly enhances the accuracy of the light-based locations. It also finally provides a quantifiable measurement of where fish like to spend their time, affirming what was known based on somewhat vague fisheries data.

Broader Impacts

Many of the tagged fish were species very popular in fisheries, such as yellowfin tuna, blue marlin, white marlin, and sailfish. Getting a more detailed idea of where these fish like to hang out or where they migrate to breed can help improve fisheries management and conservation efforts, as well as inform fishers where the best catch may be. This research also suggests that using improved fish tag data to help predict ocean heat content in models may be beneficial, as the fish may stay in these fronts even under hurricanes, where ships and other instruments have trouble going. Finally, other ecological studies of all types in the ocean may want to investigate the roles of ocean heat content in other applications, as it appears to have been an influential factor here.

Engage   

Have you noticed any patterns that wildlife near you tend to follow? How would you go about studying and quantifying them?

Discussion

No comments yet.

Post a Comment

Instagram

  • by oceanbites 2 weeks ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 1 month ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 3 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 3 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 3 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 4 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 4 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 4 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 5 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 6 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 6 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 7 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 7 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 8 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 8 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 9 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
  • by oceanbites 9 months ago
    Feeling a bit flattened by the week? So are these summer flounder larvae. Fun fact: flounder larvae start out with their eyes set like normal fish, but as they grow one of their eyes migrates to meet the other and
WP2Social Auto Publish Powered By : XYZScripts.com