Volume 1: Seabird Biodiversity and Human Activities

Jaime A. Ramos, Leonel Pereira, Jaime A. Ramos, Leonel Pereira

• Publisher: CRC Press
• Year: 2022
• Print ISBN:
  9780367498276
• eBook ISBN:
  9781000622843
• Topic: Biological Sciences
• Subtopic: Ecology
• Index: Biological Sciences

Seabirds are global travellers connecting oceans and seas all over the world, and facing multiple threats at local and global scales. Seabirds are long-lived top predators, reflecting changes at lower trophic levels, and are good models to assess ecological changes produced by human societies. Thus, world-wide collaborations are needed to understand seabird ecology and to develop effective conservation measures benefitting both humans and seabird populations.

This book provides a modern overview on seabird biodiversity studies: it begins by covering the most up-to-date techniques to study seabirds, and then focus on pragmatic issues related with interactions between seabirds and humans, the use of seabirds as ecological indicators and conservation of seabirds. It gives an updated insight on all these topics and highlights gaps that need further development for a comprehensive understanding of the relationships between seabirds and human actions.

This book covers the response of the seabird research community to a biodiversity crisis aiming to contribute towards environmental sustainability. It should provide inspiration to a wide range of professionals and students, including the much needed world-wide collaboration between research groups and practitioners. In this way seabird research and conservation provide an inspiration for the solution of global issues such as climate change.

Part C Seabirds as Ecological Indicators

Chapter 1 Seabirds as Indicators of Forage Fish Stocks

Jaime A. Ramos^1,* and Robert W. Furness²

¹ University of Coimbra, MARE - Marine and Environmental Sciences Centre, Department of Life Sciences, 3004-517 Coimbra, Portugal.

² MacArthur Green, 93 South Woodside Road, Glasgow G20 6NT, U.K.

Email: [email protected]

* Corresponding author: [email protected]

Introduction

Professional and sports fishermen around the world know that a flock of seabirds hovering above the water or plunge diving means a school of small fish underneath, possibly being chased to the surface by large predatory fish or marine mammals. Such inter-specific associations between seabirds and other marine top predators are present in all oceans, influencing population parameters and the structure of these marine communities (Veit and Harrison 2017), and have been used to navigate, locate and capture fish since historical times (Steadman 2006). The roots of using seabirds as indicators of changes in fish populations lie in the presence of these strong feeding associations.

Ecological indicators are appealing for scientists, managers, politicians and the general public (Niemi and MacDonald 2004), because they convey (often complex) information about the state of the environment in a relatively easy way, and may provide an early warning signal for ecological problems or be used as monitors for trends in ecological resources. However, to be effective, they should capture the complexity of the ecosystem concerned, and at the same time, be simple enough to be understood and cost effective to be routinely monitored (Dale and Beyler 2001). Seabirds may provide ecological indicators to show the general condition or ‘health’ of aquatic ecosystems, in which case they provide a qualitative indicator and are often referred as sentinel species (Furness and Camphuysen 1997), or they may show a specific functional relationship with a specific stressor, in which case they may be used as a quantitative ecological indicator (Piatt et al. 2007). Seabirds are suitable candidates to act as ecological indicators, because they are conspicuous top predators likely integrating ecosystems processes occurring at lower trophic levels (Frederiksen et al. 2006), easy to monitor on land and there are many long-term studies of seabird populations worldwide. However, to be ideal indicators of changes in fish stocks seabird measures should show linear relationships along the full range of fish stock variation encountered by seabirds (Dale and Beyler 2001). A first word of caution is needed because different seabird reproductive and behavioural measures are likely to respond differently to variations in forage fish, and responses vary among species (Montevecchi 1993, Furness and Camphuysen 1997).

Seabirds are long-lived, and life history predicts that they respond to a reduction in food abundance by altering their behaviour or breeding effort, in order to buffer adult survival (Stearns 1992). Their main prey, mostly small pelagic fish, are short-lived animals with strong variations in recruitment rates, which overall abundance is highly influenced by stochastic changes in oceanographic conditions (Houde 2009). Therefore natural selection provided seabirds with the ability to cope with changes in food abundance (Furness 2007). All seabird parameters, from breeding numbers to laying dates, breeding success and demographic rates are influenced by environmental variation. During years of very low food abundance, such as El Niño years in tropical areas, most of these parameters from different species may show very strong responses, to the extent that in some years seabirds may skip breeding altogether (Catry et al. 2013, Ramos et al. 2002, Cubaynes 2011), and can thus be used as sentinels of changes in marine ecosystems. However, in order to provide an informative decision as an indicator of changes in fish stocks, seabird parameters must include a wide range of environmental conditions apart from such extreme years, and the detail of the relationship between the seabird parameter and a measure of fish stock abundance is very important to consider (Cairns 1987, Piatt et al. 2007).

Since the 1990s hundreds of publications showed close relationships between seabird parameters and changes in marine environments (often in food supplies), including several reviews between 2007 and 2010 (Piatt et al. 2007, Parsons et al. 2008, Einoder, 2009, Durant et al. 2009). Einoder (2009) provided a comprehensive review on the use of seabirds as ecological indicators, important within the framework of ecosystem-based management. The traditional approach of assessing fish populations as single-stock management, i.e., considering solely the impact of fisheries, led to overfishing and the ecological deterioration of many marine ecosystems (Jackson et al. 2001). Modern views advocate that fish stocks should now be managed in relation to the structure and functionality of marine food webs (Pikitch et al. 2004). Einoder et al. (2009) outlined the limitations and uncertainties that should be considered before a seabird ecological indicator is used as a management tool: (1) the need to distinguish between the effects of fisheries and environmental change on fish stocks; (2) when selecting the most appropriate indicator species consider the spatial scale (the species should reflect the same scale that the fishery operates), life history parameters (small bodied species commonly forage at their maximum rate during good environmental conditions and are less resilient to perturbations in food conditions than large bodied species), and species foraging characteristics (low food conditions will affect more dietary specialists such as surface feeders than wide ranging and more generalist species); (3) when selecting the most important parameter as an indicator consider the temporal scale that the parameter reflects: reproductive measures such as chick growth or breeding success reflect a scale of months and are relatively easy to obtain, whereas population parameters such as adult survival reflect a scale of years to decades, but are very labourious to obtain.

The vast literature on seabird ecology clearly shows links between changes in prey abundance and behavioural, reproductive and demographic seabird measures, but as predicted by life history theory, breeding parameters such as breeding success or chick growth rate show a close relationship with food abundance, whereas other variables such as adult body condition, adult survival or number of breeding birds may not be closely related with such short-term fluctuations in food abundance (Boyd et al. 2006). Some measures such as adult body condition, evaluated as an index of body mass relative to structural body size, are easy to measure in seabird studies, but often do not show direct and clear relationships with direct or surrogate measures of food abundance (Reid et al. 2005, Piatt et al. 2007), except for years with extreme low food conditions (Paiva et al. 2013, Pereira et al. 2020). Other measures such as adult survival rates are time consuming and much more difficult to measure, and the relationship with food abundance is less clear (Davis et al. 2005, Frederiksen et al. 2005).

Whereas Einoder (2009) provided a general overview of the main factors to consider when assessing how seabirds respond to changes in the composition and availability of their prey, here we concentrate on the details of the relationship between breeding season parameters of (mostly) coastal feeding seabirds and measures of fish abundance (i.e., the functional response curve, Fig. C1.1), outlining and discussing the implications of these relationships for the monitoring of fish stocks.

Figure C1.1 Relationships between Shetland sandeel stock total biomass each year and breeding success (mean chicks per pair) of (a) Arctic Skua (Stercorarius parasiticus), (b) Black-legged Kittiwake (Rissa tridactylaand) (c) Arctic Tern (Sterna paradisaea) at Foula, Shetland, for the years when fish stock biomass and seabird breeding success were measured (1976 to 2005).

The use of seabird measures as indicators of forage fish stocks

Cairns (1987) made three important predictions for the use of seabird reproductive and behavioural measures as indicators of marine food supplies: (1) these measures would show a curvilinear relationship with variations in food supply, (2) the threshold (half-way or inflexion point in the sigmoid functional response curve) in prey abundance variation would differ for each parameter, and (3) different species should respond differently to changes in food supply, depending on their foraging behaviour and capacity to adjust time budgets. Piatt et al. (2007) examined these three predictions using up to 12 reproductive and behavioural measures of Common Murres (Uria aalge) and Black-legged Kittiwake (Rissa tridactyla) for three colonies varying in prey density over a five-year period and fo...

Table of contents

• Cover Page
• Half Title Page
• Title Page
• Copyright Page
• Preface to the Series
• Preface
• Table of Contents
• Part A: Techniques to Study Seabirds
• Part B: Seabirds Interacting with Human Activities and Infrastructures
• Part C: Seabirds as Ecological Indicators
• Part D: Actions for Seabird Conservation
• Index