Tag: marine mammal protection act

Zooming in: A closer look at bottlenose dolphin distribution patterns off of San Diego, CA

By: Alexa Kownacki, Ph.D. Student, OSU Department of Fisheries and Wildlife, Geospatial Ecology of Marine Megafauna Lab

Data analysis is often about parsing down data into manageable subsets. My project, which spans 34 years and six study sites along the California coast, requires significant data wrangling before full analysis. As part of a data analysis trial, I first refined my dataset to only the San Diego survey location. I chose this dataset for its standardization and large sample size; the bulk of my sightings, over 4,000 of the 6,136, are from the San Diego survey site where the transect methods were highly standardized. In the next step, I selected explanatory variable datasets that covered the sighting data at similar spatial and temporal resolutions. This small endeavor in analyzing my data was the first big leap into understanding what questions are feasible in terms of variable selection and analysis methods. I developed four major hypotheses for this San Diego site.

The study species: common bottlenose dolphin (Tursiops truncatus) seen along the California coastline in 2015. Image source: Alexa Kownacki.

Hypotheses:

H1: I predict that bottlenose dolphin sightings along the San Diego transect throughout the years 1981-2015 exhibit clustered distribution patterns as a result of the patchy distributions of both the species’ preferred habitats, as well as the social nature of bottlenose dolphins.

H2: I predict there would be higher densities of bottlenose dolphin at higher latitudes spanning 1981-2015 due to prey distributions shifting northward and less human activities in the northerly sections of the transect.

H3: I predict that during warm (positive) El Niño Southern Oscillation (ENSO) months, the dolphin sightings in San Diego would be distributed more northerly, predominantly with prey aggregations historically shifting northward into cooler waters, due to (secondarily) increasing sea surface temperatures.

H4: I predict that along the San Diego coastline, bottlenose dolphin sightings are clustered within two kilometers of the six major lagoons, with no specific preference for any lagoon, because the murky, nutrient-rich waters in the estuarine environments are ideal for prey protection and known for their higher densities of schooling fishes.

Data Description:

The common bottlenose dolphin (Tursiops truncatus) sighting data spans 1981-2015 with a few gap years. Sightings cover all months, but not in all years sampled. The same transect in San Diego was surveyed in a small, rigid-hulled inflatable boat with approximately a two-kilometer observation area (one kilometer surveyed 90 degrees to starboard and port of the bow).

I wanted to see if there were changes in dolphin distribution by latitude and, if so, whether those changes had a relationship to ENSO cycles and/or distances to lagoons. For ENSO data, I used the NOAA database that provides positive, neutral, and negative indices (1, 0, and -1, respectively) by each month of each year. I matched these ENSO data to my month-date information of dolphin sighting data. Distance from each lagoon was calculated for each sighting.

Figure 1. Map representing the San Diego transect, represented with a light blue line inside of a one-kilometer buffered “sighting zone” in pale yellow. The dark pink shapes are dolphin sightings from 1981-2015, although some are stacked on each other and cannot be differentiated. The lagoons, ranging in size, are color-coded. The transect line runs from the breakwaters of Mission Bay, CA to Oceanside Harbor, CA.

Results: 

H1: True, dolphins are clustered and do not have a uniform distribution across this area. Spatial analysis indicated a less than a 1% likelihood that this clustered pattern could be the result of random chance (Fig. 1, z-score = -127.16, p-value < 0.0001). It is well-known that schooling fishes have a patchy distribution, which could influence the clustered distribution of their dolphin predators. In addition, bottlenose dolphins are highly social and although pods change in composition of individuals, the dolphins do usually transit, feed, and socialize in small groups.

Figure 2. Summary from the Average Nearest Neighbor calculation in ArcMap 10.6 displaying that bottlenose dolphin sightings in San Diego are highly clustered. When the z-score, which corresponds to different colors on the graphic above, is strongly negative (< -2.58), in this case dark blue, it indicates clustering. Because the p-value is very small, in this case, much less than 0.01, these results of clustering are strongly significant.

H2: False, dolphins do not occur at higher densities in the higher latitudes of the San Diego study site. The sightings are more clumped towards the lower latitudes overall (p < 2e-16), possibly due to habitat preference. The sightings are closer to beaches with higher human densities and human-related activities near Mission Bay, CA. It should be noted, that just north of the San Diego transect is the Camp Pendleton Marine Base, which conducts frequent military exercises and could deter animals.

Figure 3. Histogram comparing the latitudes with the frequency of dolphin sightings in San Diego, CA. The x-axis represents the latitudinal difference from the most northern part of the transect to each dolphin sighting. Therefore, a small difference would translate to a sighting being in the northern transect areas whereas large differences would translate to sightings being more southerly. This could be read from left to right as most northern to most southern. The y-axis represents the frequency of which those differences are seen, that is, the number of sightings with that amount of latitudinal difference, or essentially location on the transect line. Therefore, you can see there is a peak in the number of sightings towards the southern part of the transect line.

H3: False, during warm (positive) El Niño Southern Oscillation (ENSO) months, the dolphin sightings in San Diego were more southerly. In colder (negative) ENSO months, the dolphins were more northerly. The differences between sighting latitude and ENSO index was significant (p<0.005). Post-hoc analysis indicates that the north-south distribution of dolphin sightings was different during each ENSO state.

Figure 4. Boxplot visualizing distributions of dolphin sightings latitudinal differences and ENSO index, with -1,0, and 1 representing cold, neutral, and warm years, respectively.

H4: True, dolphins are clustered around particular lagoons. Figure 5 illustrates how dolphin sightings nearest to Lagoon 6 (the San Dieguito Lagoon) are always within 0.03 decimal degrees. Because of how these data are formatted, decimal degrees is the easiest way to measure change in distance (in this case, the difference in latitude). In comparison, dolphins at Lagoon 5 (Los Penasquitos Lagoon) are distributed across distances, with the most sightings further from the lagoon.

Figure 5. Bar plot displaying the different distances from dolphin sighting location to the nearest lagoon in San Diego in decimal degrees. Note: Lagoon 4 is south of the study site and therefore was never the nearest lagoon.

I found a significant difference between distance to nearest lagoon in different ENSO index categories (p < 2.55e-9): there is a significant difference in distance to nearest lagoon between neutral and negative values and positive and neutral years. Therefore, I hypothesize that in neutral ENSO months compared to positive and negative ENSO months, prey distributions are changing. This is one possible hypothesis for the significant difference in lagoon preference based on the monthly ENSO index. Using a violin plot (Fig. 6), it appears that Lagoon 5, Los Penasquitos Lagoon, has the widest variation of sighting distances in all ENSO index conditions. In neutral years, Lagoon 0, the Buena Vista Lagoon has multiple sightings, when in positive and negative years it had either no sightings or a single sighting. The Buena Vista Lagoon is the most northerly lagoon, which may indicate that in neutral ENSO months, dolphin pods are more northerly in their distribution.

Figure 6. Violin plot illustrating the distance from lagoons of dolphin sightings under different ENSO conditions. There are three major groups based on ENSO index: “-1” representing cold years, “0” representing neutral years, and “1” representing warm years. On the x-axis are lagoon IDs and on the y-axis is the distance to the nearest lagoon in decimal degrees. The wider the shapes, the more sightings, therefore Lagoon 6 has many sightings within a very small distance compared to Lagoon 5 where sightings are widely dispersed at greater distances.

 

Bottlenose dolphins foraging in a small group along the California coast in 2015. Image source: Alexa Kownacki.

Takeaways to science and management: 

Bottlenose dolphins have a clustered distribution which seems to be related to ENSO monthly indices, and likely, their social structures. From these data, neutral ENSO months appear to have something different happening compared to positive and negative months, that is impacting the sighting distributions of bottlenose dolphins off the San Diego coastline. More research needs to be conducted to determine what is different about neutral months and how this may impact this dolphin population. On a finer scale, the six lagoons in San Diego appear to have a spatial relationship with dolphin sightings. These lagoons may provide critical habitat for bottlenose dolphins and/or for their preferred prey either by protecting the animals or by providing nutrients. Different lagoons may have different spans of impact, that is, some lagoons may have wider outflows that create larger nutrient plumes.

Other than the Marine Mammal Protection Act and small protected zones, there are no safeguards in place for these dolphins, whose population hovers around 500 individuals. Therefore, specific coastal areas surrounding lagoons that are more vulnerable to habitat loss, habitat degradation, and/or are more frequented by dolphins, may want greater protection added at a local, state, or federal level. For example, the Batiquitos and San Dieguito Lagoons already contain some Marine Conservation Areas with No-Take Zones within their reach. The city of San Diego and the state of California need better ways to assess the coastlines in their jurisdictions and how protecting the marine, estuarine, and terrestrial environments near and encompassing the coastlines impacts the greater ecosystem.

This dive into my data was an excellent lesson in spatial scaling with regards to parsing down my data to a single study site and in matching my existing data sets to other data that could help answer my hypotheses. Originally, I underestimated the robustness of my data. At first, I hesitated when considering reducing the dolphin sighting data to only include San Diego because I was concerned that I would not be able to do the statistical analyses. However, these concerns were unfounded. My results are strongly significant and provide great insight into my questions about my data. Now, I can further apply these preliminary results and explore both finer and broader scale resolutions, such as using the more precise ENSO index values and finding ways to compare offshore bottlenose dolphin sighting distributions.

Sea Otter Management in the U.S.

By Dominique Kone, Masters Student in Marine Resource Management

Since the first official legal protections in 1911, the U.S. has made great strides in recovering sea otter populations. While much of this progress is due to increased emphasis on understanding sea otter behavior, biology, and ecology, there are also several policies that have been just as instrumental in making sea otter conservation efforts successful. Here, I provide a brief overview of the current legal and regulatory policies used to manage sea otters in the U.S. and explain why having a base understanding of these tools can help our lab as we look into the potential reintroduction of sea otters to the Oregon coast.

Sea otter with pup, Prince William Sound, Alaska. Source: Patrick J. Endres

When we talk about sea otter management in the U.S., the two most obvious laws that come to mind are the Marine Mammal Protection Act (MMPA) and the Endangered Species Act (ESA). In short, the MMPA seeks to prevent the take – including kill, harass, capture, or disturb – or importation of marine mammals and marine mammal products[1]. While the ESA seeks to protect and recover imperiled species – not just marine mammals – and the ecosystems which they depend upon[2]. Both laws are similar in the sense that their primary objectives are to protect and recover at-risk species. However, marine mammals will always be protected under the MMPA, but will only be protected under the ESA if the species is considered threatened or endangered.

On the federal level, the U.S. Fish and Wildlife Service (the Service) is primarily responsible for managing sea otter populations. In the U.S., we manage sea otter populations as five distinct stocks, which differ in their population size and geographic distribution – located in California, Washington, and Alaska state waters (Fig. 1). Because sea otters are divided into these single stocks, management decisions – such as recovery targets or reintroductions – are made on a stock-by-stock basis and are dependent on the stock’s population status. Currently, two of these stocks are federally-listed as threatened under the ESA. Therefore, these two stocks are granted protection under both the ESA and MMPA, while the remaining three stocks are only protected by the MMPA (at the federal level; state management may also apply).

Figure 1. Distribution (approximations of population centers) of sea otter stocks in the U.S. (SW = Southwest Alaskan; SC = Southcentral Alaskan; SE = Southeast Alaskan; WA = Washington, SCA = Southern/Californian)

While the MMPA and ESA are important federal laws, I would be remiss if I didn’t mention the important role that state laws and state agencies have in managing sea otters. According to the MMPA and ESA, if a state develops and maintains a conservation or recovery program with protections consistent with the standards and policies of the MMPA and/or ESA, then the Service may transfer management authority over to the state1,2. However, typically, the Service has opted to manage any stocks listed under the ESA, while states manage all other stocks not listed under the ESA.

Sea otter management in the states of Washington and California is a clear example of this dichotomy. The Washington sea otter stock is not listed under the ESA, and is therefore, managed by the Washington Department of Fish and Wildlife (WDFW), which developed the stock’s recovery plan[3]. In contrast, sea otters along the California coast are listed as threatened under the ESA, and the Service primarily manages the stock’s recovery[4].

Interestingly, sea otter management in Alaska is an exception to this rule. The Southeast and Southcentral sea otter stocks are not listed under the ESA, yet are still managed by the Service. However, the state recognizes sea otters as a species of greatest conservation need in the state’s Wildlife Action Plan, which acts as a recommendation framework for the management and protection of important species and ecosystems[5]. Therefore, even though the state is not the primary management authority for sea otters by law, they still play a role in protecting Alaskan sea otter populations through this action plan.

Table 1. Federal and state listing status of all sea otter stocks within U.S. coastal waters.

States have also implemented their own laws for protecting at-risk species. For instance, while the Washington sea otter stock is not listed under the ESA, it is listed as endangered under Washington state law4. This example raises an important example demonstrating that even if a stock isn’t federally-listed, it may still be protected on the state level, and is always protected under the MMPA. Therefore, if the federal and state listing status do not match, which is the case for most sea otter stocks in the U.S. (Table 1.), the stock still receives management protection at some level.

So why does this matter?

Each of the previously mentioned laws are prohibitive in nature, where the objectives are to prevent and discourage activities which may harm the stock of interest. Yet, agencies may grant exceptions – in the form of permits – for activities, such as scientific research, translocations, commercial/recreational fisheries operations, etc. The permit approval process will oftentimes depend on: (1) the severity or likelihood of that action to harm the species, (2) the species’ federal and state listing status, and (3) the unique approval procedures enforced by the agency. Activities that are perceived to have a high likelihood of harming a species, or involve a species that’s listed under the ESA, will likely require a longer and more arduous approval process.

A sea otter release in Monterey Bay, California. Source: Monterey Bay Aquarium Newsroom.

Understanding these various approval processes is vitally important for our work on the potential reintroduction of sea otters to Oregon because such an effort will no doubt require many permits and a thoughtful permit approval process. Each agency may have their own set of permits, administrative procedures, and approval processes. Therefore, it behooves us to have a clear understanding of these various processes relative to the state, agency, or stock involved. If, hypothetically, a stock is determined as a suitable candidate for reintroduction into Oregon waters, having this understanding will allow us to determine where our research can best inform the effort, what types of information and data are needed to inform the process, and to which agency or stakeholders we must communicate our research.

 

References:

[1] Marine Mammal Protection Act of 1972

[2] Endangered Species Act of 1973

[3] State of Washington. 2004. Sea Otter Recovery Plan. Washington Department of Fish and Wildlife: Wildlife Program

[4] U.S. Fish & Wildlife Service. 2003. Final Revised Recovery Plan for the Southern Sea Otter (Enydra lutris nereis).

[5] Alaska Department of Fish and Game. 2015. Alaska wildlife action plan. Juneau.