Abstract
Intense fishing pressure and climate change are major threats to coastal
fisheries. Larimichthys crocea (large yellow croaker) is a
long-lived fish, which performs seasonal migrations from its spawning
and nursery grounds along the coast of the East China Sea (ECS) to
overwintering grounds offshore. This study used length-based analysis
and habitat suitability index (HSI) model to evaluate current
life-history parameters and overwintering habitat suitability ofL. crocea , respectively. We compared both life-history parameters
and overwintering HSI between recent (2019) and historical (between 1971
to 1982) to analyze the fishing pressure and climate change effects on
the overall population and overwintering phase of L. crocea . In
the context of overfishing, the length-based analysis indicated serious
overfishing of L. crocea , characterized by reduced catch yield,
size truncation, constrained distribution, and advanced maturation in
the ECS, namely recruitment bottleneck. In the context of climate
change, the overwintering HSI modeling results indicated that climate
change has led to decreased sea surface temperature during L.
crocea overwintering phase over the last half-century, which in turn
led to area decrease and an offshore-oriented shifting of optimal
overwintering habitat of L. crocea . The fishing-caused size
truncation may have constrained the migratory ability and distribution
of L. crocea subsequently led to the mismatch of the optimal
overwintering habitat against climate change background, namely habitat
bottleneck. Hence, while heavily fishing was the major cause of L.
crocea fishery collapse, climate-induced overwintering habitat
suitability may have intensified the fishery collapse of L.
crocea population. It is important for management to take both
overfishing and climate change issues into consideration when developing
stock enhancement activities and policy regulations, particularly for
migratory long-lived fish that share a similar life history to L.
crocea . Combined with China’s current restocking and stock enhancement
initiatives, we propose recommendations for future restocking ofL. crocea in China.
Key words: Larimichthys crocea, overfishing, climate
change, length-based analysis, HSI model, East China Sea.
INTRODUCTION
Globally, heavily fishing activities and climate change are rapidly
reducing the abundance of many marine organisms and increasing the
likelihood of species extinction (Hoegh-Guldberg and Bruno 2010, Cinner
et al. 2012, Burgess et al. 2013, Payne et al. 2016). For instances,
intensive fishing and climate change had caused overfishing and declined
catches in Canada, Iceland, and China (Pauly et al. 2011, Du et al.
2014, Liang and Pauly 2017). In addition, ‘fishing-induced life-history
variation’ at population level, together with ‘fishing down the marine
food web’ and/or ‘trophic cascade’ at ecosystem level have been observed
and demonstrated in variety contexts through theoretical and empirical
evidence (Essington et al. 2006, Gascuel et al. 2014, Kuparinen et al.
2016, Szuwalski et al. 2017). Previous studies showed that fishing
pressures and climate change can affect the (i) the life-history
strategy of individuals, via impacts on physiology, morphology and
behavior (Ba et al. 2016, Olafsdottir et al. 2016); (ii) the population
dynamics, via changes to key population processes throughout an
organism’s life-history and habitat suitability (Perry et al. 2005).
Hence, bottlenecks of any life-history stage (e.g. spawning, hatching,
larval survival, recruitment settlement, growth, and death), and habitat
suitability can cause overfishing of exploited species. In this context,
recruitment bottleneck and habitat bottleneck are probably the most
widely known bottlenecks (Almany and Webster 2006, Caddy 2011).
Correspondingly, the potential cause of overfishing is mismanagement
because of a poor understanding of recruitment bottleneck and habitat
bottleneck that constrain the productivity of the overall population.
Fishing alters the size structure throughout remove large fish due to
the size-selective of gears. Heavily fishing can diminish the ability of
fish to reproduce (recruitment overfishing) and/or constrain the overall
recruitment ability before they can fully realize their growth potential
(growth overfishing) (Diekert 2012) via size truncation effect (STE)
(Berkeley et al. 2004, Ottersen et al. 2006, Froese et al. 2008,
Langangen et al. 2019). This effect states that population shifts with
decreasing body sizes and advancing maturation characteristic of the
life-history changes induced by fishing (Berkeley et al. 2004, Anderson
et al. 2008, Bell et al. 2015). Hence, fishing for juveniles (before
reaching first maturity) and mega-spawner can weaken the reproductive
potential of a fish stock, called ‘recruitment bottleneck’ (Doherty et
al. 2004). Such bottlenecks are visible in respective long-term time
series and are a common cause of collapse in intense fished stocks, for
example in Western cod, Pacific rockfish and North Sea ground fish
(Harvey et al. 2006, Poulsen et al. 2007, Froese et al. 2008).
The impacts of overfishing do not occur in isolation, but against a
background of existing climate change-caused environmental conditions
shift (Graham et al. 2011, Johnson et al. 2011). In general, species’
distribution patterns are relative with both life-history strategies
(Anderson et al. 2013) and physiology tolerance on environmental
variables, such as sea surface temperature (SST), chlorophyll-a
concentration (Chl-a), sea surface salinity (SSS), currents et al. (Guan
et al. 2013, Yu and Chen 2018). Environmental shift can selectively
affect the habitat suitability of target species (Farrell et al. 2008).
Lower habitat suitability of any life-history stage can lead to
species-specific ‘habitat bottleneck’ and latter can have large
consequences for climate-induced fishery phenomena, for examples,
Norwegian herring, Maine cod and Mid-Atlantic Bight winter flounder
(Bell et al. 2015, Pershing et al. 2015).
Heavily fishing activities and environmental conditions shift can have
combined effects on fishery collapse, especially for long-lived species
(Rose 2004, Hsieh et al. 2009). Specifically, some studies suggested
that long-lived species are expected to have slower demographic response
to climate change (Berteaux et al. 2004, Wilson et al. 2010).
Additionally, fishing-caused STE can exacerbate long-lived fish
degradation via diminishing ‘bet-hedging’ capacity, including the
ability of migrate and avoid poor areas, having flexibility in spawning
times and locations, and production of high-quality offspring that
survive in a broader suite of environmental conditions, for adapting to
rapid climate change (Bell et al. 2015). However, there is no relevant
examples exist that demonstrate the STE and the climate-induced effects
on long-lived migratory fish in the most heavily fishing (and minimally
managed) marine ecosystem in the world: the East China Sea (ECS). To
fill the knowledge gaps, we require a species that (i) under intensive
fishing pressure; (ii) has specific habitat requirements; (iii) the
habitat of which is affected by rapid climate-induced habitat
suitability variation; (iv) can be reliably counted by a long-term field
survey.
In the following, we provide an appropriate example by discussing
changes in specific population dynamic of
an overexploited, long-lived,
migratory fish in the ECS, the large yellow croaker (Larimichthys
crocea ). The collapse of L. crocea represents an
interesting example to explore both heavily fishing and climate change
on overall population: (i) L. crocea ranked top among the four
major marine economical fishes in China in last century (Zhang et al.
2010) but encountered collapse since the 1980s. The latest International
Union for Conservation of Nature (IUCN) Red List of Threatened Species
labelled L.croce s as ‘critically endangered (CR)’ (Liu et al.
2020); (ii) L. crocea is a long-lived species with maximum age 21
years in 1960s (Zhang et al. 2017). Accompanied by population collapse,
the L. crocea population in the ECS is characterized by decreased
maximum age and body size, and advanced maturation (Ye et al. 2012).
(iii) L. crocea is a migratory fish which conduct climatic
migrations and gametic migrations between offshore water and coastal
water during autumn-winter and spring-summer respectively (Fig. 1A).