COMBINING HISTORICAL DATA AND SPECIES DISTRIBUTION MODELS TO FILL INFORMATION GAPS FOR SPECIES WITH VARIOUS LEVELS OF DEPLETION

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A brief history of marine mammal exploitation

Easily accessible coastal species of marine mammals were particularly vulnerable to human exploitation and have been for millennia the target of aboriginal subsistence for the meat, oil, bones and fur they provide. Pinnipeds, that need to come to land for reproduction, were targeted particularly early (e.g. Giles-Pacheco et al., 2008). But some whale species coming close to shore for part of their life-cycles were also accessible. It is not clear when exactly whaling has started, but one of the earliest testimony of what appears to be active hunting is the representation of whaling scenes in petroglyphs dated from 6,000-1,000 years Before Present (BP) in Bangu-dae, Ulsan, South Korea (Lee & Robineau, 2004) (Figure I-4). These carvings represent cetaceans (identified as Balaenidae, Balaenopteridae and sperm whales) apparently hunted from boats with nets, harpoons and floats (Figure I-5). This suggests that the Neolithic populations living along the coast of Korea were actively hunting whales, and with relatively simple technologies.

Strategy for reviewing historical data

In order to improve our efficiency in finding historical records of occurrence in the literature, we settled on a strategy for reviewing them. First, we looked for existing reviews or compilations of historical/pre-historical data for a particular species. This entailed searching specifically for references on the species in question, through scientific papers and academic reports. Then, we searched for records associated with particular areas, focusing on areas outside the species’ current EOO either at the edge of the range or in areas which represent “gaps” in the current distribution. Indeed, if range contractions did occur for these species, such areas are the most likely regions for those contractions to have taken place. Finally, records of historical occurrence encountered opportunistically during the review process (e.g., records for walrus found when reviewing the history of bowhead whaling) were also included in the dataset. I entered the records into a database capturing information on the species, the location, the time, record details and the reference in which it was found.
We focused on records within the past 10,000 years (beginning of the Holocene period) to reduce the confounding effects of climate change during the last ice age and so to focus primarily on the impact of human exploitation on marine mammal’s range shift. We looked for historical and pre-historical records of species occurrence from three types of sources: 1) archaeological and zooarchaeological remains (from 10,000 years before present to today); 2) historical anecdotes, particularly from marine travel records (over the last few hundred years); and 3) statistics from the whaling and sealing industries (from the late 18th to the early 20th century).
While the combined effort of members of the MORSE project enabled the collection of historical records for more than twenty species, I chose to present the results for a selection of species, for which we have collected more than 30 records of past occurrence, which concerns ten marine mammal species, in six families. I list these species in Table II-1, providing a short summary on the history of their exploitation and current IUCN Red List status.

Caribbean monk seal (Monachus tropicalis)

Historical occurrence data for the Caribbean monk seal were extracted from a review by Adam and Garcia (2003) where localities of the species past occurrence were derived from historical, archaeological, paleontological and place names data. The full table including details on each record and references was not reproduced here, but it can be found in this review (Adam & Garcia, 2003, p.311:317). The data indicate that this species inhabited isolated islands and reefs throughout the Greater and Lesser Antilles, in the southern Caribbean Sea along the northern coast of central and South America, in the Gulf of Mexico and as far north as the coast Georgia in southeastern America (Figure II-2).

Mediterranean monk seal (Monachus monachus)

An extensive review has been performed for the Mediterranean monk seal as part of an internship by Christel Vidaller, supervised by Ana Rodrigues and myself, which aimed at mapping the historical breeding distribution of the species. A paper is being written based on this review (Vidaller et al., In Prep), which includes detailed information about the reviewing methods, the criteria for identifying monk seal reproduction areas, the complete list of records and associated references, and a discussion of the results. The location of historical records indicates that the species used to breed throughout the Mediterranean basin, in the eastern Black Sea, in the coasts of Senegal, Mauritania and Western Sahara, and in the Cape Verde, Canary and Madeira archipelago (Figure II-2). Gaps around the Lybian and Egyptian coasts are mostly attributed to the inability to find historical sources rather than to the species’ absence in these areas.

North Pacific right whale (Eubalaena japonica)

Sightings and catches of North Pacific right whales in the WWH dataset occurred between 1822 and 1904, with the bulk of exploitation in the 1840’s. Whaling records indicate that NPRW were historically concentrated in the summer in five main areas: the Gulf of Alaska, the southeastern Bering Sea, east of Kamchatka and the Kuriles, the Sea of Okhotsk and the Sea of Japan (Figure II-5). Records in the Gulf of Alaska, southeast of Kamchatka and in the Sea of Japan are not included in the current EOO of the species, indicating that the species used to occupy a much broader range than it does today.

Humpback whale (Megaptera noveaengliae)

Humpback whales were a secondary target of American pelagic whalers, hunted throughout their range, in winter on their calving grounds in tropical and subtropical waters (e.g. Baja California, coast of northwest South America, coast of Angola, Cape Verde, Lesser Antilles), in summer in their feeding grounds (e.g. northwest North Pacific, Bering sea), and along the species’ migration routes (e.g. mid North Atlantic, Gulf of Alaska, southern coasts of Chile and Argentina) (Figure II-8). Hunting for humpbacks occurred during almost the entire commercial whaling period, with encounters reported from 1792 to 1902.

Improving understanding of the ecology of depleted species

In his chapter on the walrus in the Encyclopedia of Marine Mammals, Kastelein describes the species’ ecology in these terms: “The walrus is found in the Arctic, where its distribution is limited by the availability of shallow water foraging grounds and thickness of ice” (Kastelein, 2009). And indeed, it is a well-accepted fact that walruses are associated with sea ice for most of their lives (Fay, 1982; Moore & Huntington, 2008). Hence, the presence of a single walrus in the Orkneys in March 2013, way further south than the species’ range, raised much attention and was interpreted as the wandering of a lost individual. When reviewing the presence of the species in this area, one might find that its presence was mentioned in Scotland in the 19th century (Boece, 1821; Southwell, 1881). However, this is not sufficient evidence that the species was regularly found in this area, where the habitat is very different from the ice-covered regions currently used by the species. Only a larger-scale perspective on the species former distribution may bring further context to the possibility that it may have once inhabited terrestrial habitat further south of its current distribution. Here, we present records of the species occurrence outside of its current range and spanning several millennia, including in Iceland, Scotland, the Netherlands, the Gulf of St Lawrence and the eastern coast of Canada south of 50°N. In the North Pacific, a single record was found, referring to a walrus bank discovered in 1648 along the eastern coast of Kamchatka, south of its current distribution. Many of these records are not associated with vagrancy, as testified by the use of words describing abundance of the species (“abundant”, “herds”, “banks”) or references to hunting traditions.
The accumulation of historical records south of the current distribution of the species raises interesting questions: Did the walrus once inhabited these ice-free areas? Did we lose memory of its presence here? Would the walrus be able to recolonize this habitat now that the threat of hunting is gone?
Historical records seem to support the hypothesis that historical populations of walruses were able to live in these areas. In 2010, an « extra-limital » walrus found in the Faroe islands originated from the Svalbard population and returned back to it, suggesting not a lost individual but one exploring (Born et al., 2014).
Potential effect of climate change (e.g. colder climate, little ice age period) could explain to some extent a range shift for this species, but the historical data span a broad period of time and reconstruction of past extent of the ice sheet during the Holocene don’t support the idea that ice was covering areas this far south in the North Atlantic (Dyke & Prest, 1987).
Moreover, observations of walrus in Norway have been increasing (despite general climatic warming), consistent with a recolonization of an ancient range (Gjertz et al., 1993).
References to the heavy exploitation and depletion of hunting grounds support the hypothesis of a range contraction due to overexploitation of the populations. Two processes might explain the depletion of the southernmost populations: On one hand, walruses inhabiting ice free areas may have been more exposed and more impacted by human exploitation than those inhabiting the ice sheet. On the other hand, walruses may have found shelter from human pressure by moving north and using only the most remote areas of their distribution. If the walrus exhibit some level of philopatry (Sonsthagen et al., 2012), the loss of lineages associated with ice-free areas could have resulted in the loss of this behavior in the population. Genetic and morphological data indicate that the walruses of the Gulf of St Lawrence were a distinct group. Range contraction in this area may thus be associated with loss of diversity (and possibly of a phenotype more adapted to southern latitudes) (McLeod et al., 2014). In the end, this review of historical data brings context to our knowledge of the ecology of the species and questions current concerns about the resilience of walrus populations to climate change (Moore & Huntington, 2008).

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Mapping the historical envelope of species’ occurrence

The simplest spatial representation of the historical distribution of a species is an envelope which encompasses all the known occurrences of the species.
Here, I present two examples of such historical envelopes of occurrence, for the summer range of the North Atlantic right whale (which was already heavily depleted by the 19th century and for which we have little information on its historical range), and for the Caribbean monk seal (which got extinct by the mid-20th century). For both species, I draw an envelope around the historical occurrence data mapped in Figure II-2 and Figure II-4, using a smoothed convex hull polygon (with a detail level of 5% for a closer fit of the data) (Figure II-10, Figure II-11). For the North Atlantic right whale, I also considered information on the current distribution of the species, by including the southeastern coast of the US in the envelope.
The resulting envelopes of occurrence give simplistic views of the historical range of the species, but are nonetheless informative of the level of depletion when compared to the current range of the species (overall extirpation for the Caribbean monk seal, restriction to the eastern coast of North America for the North Atlantic right whale in summer). This gives an idea of regions from which the species has become extinct. If multiple species are considered within the same area, it is useful to quantify and map the level of human impact. Mapping the extinct part of species’ ranges is useful for understanding the composition of past communities in these regions, and is a useful context to zooarchaeologists who try to identify specimens from a pool of candidate species, which is needed to counteract the shifting baseline syndrome.

Table of contents :

I. INTRODUCTION
SHIFTING BASELINES AND THE RISE OF “HISTORICAL ECOLOGY”
The shifting baseline syndrome
Implications for conservation
Applied historical ecology
MARINE HISTORICAL ECOLOGY AND THE OVEREXPLOITATION OF MARINE RESOURCES
Marine historical ecology
Consequences of the overexploitation of marine resources
OPPORTUNITIES FOR SETTING APPROPRIATE POPULATION BASELINES
Historical occurrence data
Methodological opportunities for setting baselines from historical data
FOCUS ON MARINE MAMMALS
A brief history of marine mammal exploitation
Marine mammals as an interesting case study
OBJECTIVES
STRUCTURE
II. USING SPECIES’ HISTORICAL OCCURRENCE DATA TO INVESTIGATE RANGE CONTRACTIONS: A REVIEW FOR TEN MARINE MAMMAL SPECIES AND POSSIBLE APPLICATIONS
ABSTRACT
INTRODUCTION
STRATEGY FOR REVIEWING HISTORICAL DATA
SPECIES REVIEWS
Walrus (Odobenus rosmarus)
Caribbean monk seal (Monachus tropicalis)
Mediterranean monk seal (Monachus monachus)
Bowhead whale (Balaena mysticetus)
North Atlantic right whale (Eubaleana glacialis)
North Pacific right whale (Eubalaena japonica)
Southern right whale (Eubalaena australis)
Gray whale (Eschrichtius robustus)
Humpback whale (Megaptera noveaengliae)
Sperm whale (Physeter macrocephalus)
CHALLENGES AND OPPORTUNITIES IN HISTORICAL OCCURRENCE DATA
Archaeological remains
Historical accounts
Industry statistics
APPLICATIONS OF SPECIES’ HISTORICAL OCCURRENCE DATA
Improving understanding of the ecology of depleted species
Mapping the historical envelope of species’ occurrence
Mapping the sequence of historical depletion of a species
Modeling a species’ historical distribution based on its environmental preferences
DISCUSSION AND CONCLUSION
III. COMBINING HISTORICAL DATA AND SPECIES DISTRIBUTION MODELS TO FILL INFORMATION GAPS FOR SPECIES WITH VARIOUS LEVELS OF DEPLETION
ABSTRACT
INTRODUCTION
Three species, three histories of exploitation
Challenges and Opportunities
MATERIAL AND METHODS
Nineteenth century whaling data
Environmental data
Species distribution models
RESULTS AND DISCUSSION
Limitations and caveats
Humpback whale (Megaptera novaeangliae)
Bowhead whale (Balaena mysticetus)
Gray whale (Eschrichtius robustus)
Interest of the modeling approach
CONCLUSION
APPENDIX
Appendix S1. Model selection, performance and validation
Appendix S2. Fitted functions of the species-environment relationships produced by the BRT
IV. HISTORICAL SUMMER DISTRIBUTION OF THE ENDANGERED NORTH ATLANTIC RIGHT WHALE (EUBALAENA GLACIALIS): A HYPOTHESIS BASED ON ENVIRONMENTAL PREFERENCES OF A CONGENERIC
ABSTRACT
INTRODUCTION
MATERIAL AND METHODS
Historical records of North Pacific right whales
Environmental data
Species distribution modeling
Historical records of North Atlantic right whales
RESULTS
Historical records of North Pacific right whales
Species distribution model
Model predictions
Historical records of North Atlantic right whales
DISCUSSION
Assumptions and caveats
Comparison between the model predictions and species records in the North Atlantic
CONCLUSIONS
APPENDICES
Appendix S3: Fitted functions
Appendix S6: Extended discussion
V. HOW MANY RIGHT WHALES WERE THERE IN THE NORTH ATLANTIC BEFORE COMMERCIAL WHALING? AN ESTIMATE BASED ON NORTH PACIFIC WHALING RECORDS
ABSTRACT
INTRODUCTION
METHODS AND RESULTS
Data on the distribution of catches of North Pacific right whales
Environmental predictors
Abundance modeling in the North Pacific
Model validation
Estimates of total population size in the North Pacific
Estimates of total population size in the North Atlantic
DISCUSSION
Uncertainties and assumptions
Agreement between predictions, the historical record and genetic analyses
Implications for the present and future of the North Atlantic right whale
CONCLUSION
APPENDICES
VI. DISCUSSION
RECONSTRUCTING THE PAST: FROM DESCRIPTION TO PREDICTION
Interpretation of historical anecdotes
Estimates of historical catches
Maps of historical occurrence
Envelopes of historical occurrence
Predictive models of historical distribution
Predictive models of historical abundance
LESSONS LEARNED FROM THE ANALYSIS OF HISTORICAL DATA
Understanding species’ habitat preferences and how they have been affected by humans
Understanding past distributions and anthropogenic range contractions
Understanding past abundances and human-caused population depletions
BIODIVERSITY CONSERVATION IN A CHANGING WORLD
How to define the historical baseline?
Is the historical baseline an achievable/desirable target for conservation?
REFERENCES

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