Population Trends


Ecosystem Changes

2 Baltic-diverse


Research in the Lotze Lab @ Dalhousie University focuses on human-induced changes in marine populations, communities and ecosystems. This includes past, present and potential future human impacts in the ocean, such as exploitation, habitat alteration, nutrient pollution, and climate change. We aim to understand how these individual and cumulative drivers have altered – or will alter – the abundance of populations, biodiversity patterns, species interactions, the underlying structure and functions of marine ecosystems and the services they provide for human well-being.

Students and post-doctoral fellows are engaged in analyzing:

  • long-term historical and potential future changes in different populations and regions,
  • large-scale patterns of change across gradients of human impacts,
  • cumulative effects of multiple human drivers,
  • the consequences for ecosystem structure, functions and services, and
  • recovery of depleted species and degraded ecosystems.

To approach these topics, we use a combination of large-scale field surveys, factorial laboratory experiments, historical literature studies, analysis of large data sets, and ecological modeling.


  • News_NLM model

    Nitrogen loading is a principal factor associated with the decline in eelgrass bed health and cover in estuaries worldwide. In this paper, we applied a nitrogen loading model to estimate annual inputs of total dissolved nitrogen from point and nonpoint sources in 7 estuaries in Atlantic Canada. Our results provide new information on nitrogen loading in a region with mainly forested watersheds and comparatively low human impacts.

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  • Eddy-etal_2015_ICES_2

    Invertebrate fisheries are increasing around the world, yet their consequences are largely unknown, impairing ecosystem-based management. This study shows that lobster, abalone and urchin fisheries have considerable effects on other species and the marine ecosystem as a whole, particularly at current high exploitation levels that exceed those that would produce maximum sustainable yield. Thus, reducing exploitation would benefit both target catches and the environment, a win–win situation.

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  • Paleontological baselines

    The fossil record provides rich information on past extinctions in the world’s oceans. This new collaborative study shows how we can use such information to predict which living species today are inherently more vulnerable and at a higher risk of extinction than others. Mapping their distribution globally identifies regions with high intrinsic risk. Some of these regions are also strongly affected by current human activity or climate change, and may be hotspots of future extinctions.

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  • Ocean Literacy in Nova Scotia

    This study used a quiz and survey to assess the level of ocean literacy in more than 700 public school students in grades 7-12 in Nova Scotia. Results indicate relatively low levels of ocean knowledge and a positive link between knowledge and valuation of the marine environment and interest in ocean-related jobs and careers. This suggests that improving public awareness about the ocean can benefit the environment, economy, and society.


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  • Expansion of Hagfish Fisheries in Atlantic Canada and Worldwide

    Hagfish have been commercially fished in Asia since the 1940s. This new study shows that after local stock depletion hagfish fisheries expanded around the world with some serial depletion patterns as in sea urchin and sea cucumber fisheries. In Atlantic Canada, hagfish landings and fishing effort increased 24-fold over the past 20 years with strong spatial expansion. The sustainability of current hagfish fisheries is questioned given the limited knowledge, assessments and regulations.

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  • Predator decline leads

    Exploitation has caused widespread declines in marine predators, such as large sharks. It has long been assumed that this may destabilise marine communities, yet empirical evidence has been lacking. In this new study, we used a community matrix model to analyze three indices of stability in a coastal fish community and found significantly decreasing stability with predator depletion. These results have important implications for the conservation and management of predators in our oceans.

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  • What Recovery of Exploited Marine

    In this new book Marine Historical Ecology in Conservation, edited by JN Kittinger, LE McClenachan, KB Gedan, and LK Blight, the authors explore how we can apply historical knowledge to manage for the future. In Chapter 2, Heike reviews trends in the recovery and non-recovery across a range of marine species and their major drivers. She also assesses the management successes and failures and how knowing the past can improve current and future conservation efforts.

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  • 7_Lotze etal 2014_THE SEA

    Another new Book on Marine Ecosystem-based Management edited by MJ Fogarty and JJ McCarthy in the Series THE SEA, Volume 16. In Chapter 2, Heike together with historian Richard Hoffmann and archaeologist Jon M. Erlandson describe the history of fishing and how people throughout history responded to resource depletion. It shows how different management measured evolved and what we can learn from their successes and failures.

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  • marinecomecol_2

    Check out this new Marine Community Ecology and Conservation Book edited by MD Bertness, JF Bruno, BR Silliman and JJ Stachowicz. In Chapter 8, Heike and co-author Loren McClenachan describe the origin and development of marine historical ecology, synthesize what and how we can learn from different disciplines and data, and discuss how we can apply this historical knowledge in science, management, conservation and education.

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  • The abundance of sharks and rays can decline considerably with fishing, but assessing the drivers of community changes can be complicated by species interactions and variations in vulnerability to fishing. This study used data from five trawl surveys conducted between 1948 and 2005 to evaluate long-term trends in elasmobranch communities in the Adriatic Sea. Since 1948, catch rates have declined by > 94% and 11 species ceasing to be detected.

  • Heike Lotze & Boris Worm received this year’s Peter Benchley Award for Excellence in Science. Through their extensive body of work they have significantly increased the world’s knowledge about the changing abundance and diversity of the planet’s fish and marine wildlife populations and the impact of nutrient pollution and other human activities. The awards ceremony will take place on May 15, 2013 at the Carnegie Institution in Washington, D.C.

  • Marine mammals have greatly benefitted from a shift from exploitation towards conservation. Yet while some populations have shown remarkable recoveries, others remained at low levels, continued to decline, or became extinct. This study synthesizes available data for marine mammal populations worldwide, quantifies their abundance trends and recovery status, and evaluates the link between historic population decline and recent recovery.


  • In response to declining elasmobranch populations, combined with the realization of their importance to the environment and local economies, a number of management plans have been initiated to slow and (ideally) reverse these negative trends. This paper reviews our current understanding of elasmobranch population recoveries and shows that 1) populations can recover – the earlier the better; 2) incidental fishing pressure can stall or prohibit recovery; and 3) management and conservation strategies must be multi-faceted in order to be successful.

  • In the coming century, life in the ocean will be confronted with a suite of environmental conditions that have no analog in human history. Will marine species adapt or go extinct? This study compares the patterns, drivers, and biological correlates of marine extinctions in the fossil, historical, and modern records and evaluates how this information can be used to better predict the impact of current and projected future environmental changes on extinction risk in the sea.

  • The assessment of fishery status is essential for management, yet fishery-independent estimates of abundance are lacking for most fisheries. Methods exist to infer fishery status from catches, but the most commonly used method is biased towards classifying fisheries as overexploited or collapsed and does not account for still-developing fisheries. This study introduces a revised dynamic catch-based method that overcomes these deficiencies.

  • Eutrophication in the coastal ocean can severely alter the composition of marine plants with consequences on carbon and nutrient storage and cycling as well as habitat and food provision for associated animal communities. This study used large-scale field surveys across 12 estuaries in two provinces in Atlantic Canada to quantify eutrophication-induced changes in the ecosystem structure and services of seagrass beds.


  • Check out this New Book edited by J.B.C. Jackson, Karen E. Alexander & Enric Sala. In Chapter 8 “Uncovering the Ocean’s Past” of this volume, Heike and co-authors synthesize how we can use records from palaeontology, archaeology, history, genetics, early scientific surveys and modern ecology to understand the ocean’s ecological and environmental history.

  • The Adriatic Sea is among the most human-impacted coastal ecosystems worldwide – but when did humans start to affect its marine resources? Reconstructing past changes in marine resources and food-web structure, this study illustrates the long-term and far-reaching consequences human activities can have on marine ecosystems. Resource abundance has changed since at least Roman times and accelerated in the 19th and 20th centuries. Today, most traditional marine resources are depleted, and many species are rare or extirpated leaving food webs simplified and less resilient to further perturbations.

  • Marine vegetated habitats provide essential functions and services to ocean ecosystems and human well-being. It is unclear, however, how different habitat types compare. Using large-scale field surveys and binary network models we compared the habitat and food-web structure between eelgrass and rockweed beds in Atlantic Canada, assessed their nitrogen and carbon storage services, and determined their robustness to species loss.

  • Many marine populations and ecosystems have experienced strong historical depletions, yet reports of recoveries are increasing. This study reviews how common recovery is among depleted populations and degraded ecosystems and what its magnitude, timescale and major drivers are. Learning from such recovery successes as well as failures is essential for implementing realistic conservation goals and promising management strategies.


  • Estuaries have been vital components of marine ecosystems throughout history, and for millennia, human activities have shaped estuaries more then any other part of the ocean ecosystem. A review of the timeline, magnitude and range of human-induced changes within and across six estuaries in the United States before and since European colonization aids in determining the current status and potential future trajectories of estuaries and the development of realistic management and conservation goals.

  • A study synthesizing the nature and scale of the ecological consequences of shark declines in the global ocean uncovered overall patterns and presents new evidence for the importance of shark populations to the rest of the marine world.

  • In only a few decades, most sea cucumber fisheries around the world have experienced a boom-and-bust pattern; over time, this has happened faster and further away from the main markets in Hong Kong and China. Currently, 81% of sea cucumber fisheries globally have experienced population declines due to overfishing. The findings suggest these fisheries are often unsustainable and may develop too rapidly for effective management responses.