Fishers’ Local Ecological Knowledge recovers information about the recent-past existence of a Caribbean coastal shark and ray nursery area

Technical Summary: Fishers' Local Ecological Knowledge Recovers Information about the Recent-Past Existence of a Caribbean Coastal Shark and Ray Nursery Area

Problem Statement
Elasmobranchs (sharks and batoids) are among the most threatened vertebrate taxa globally, primarily due to overfishing and habitat degradation. Their life-history strategies (K-selected, low reproductive potential) make populations slow to recover from exploitation. A critical component of their conservation is the identification and protection of nursery areas, defined by specific criteria: high density of early offspring, site fidelity, and recurrent use across years. However, these areas are globally understudied, particularly in the Mexican Caribbean. A significant barrier to understanding historical population dynamics is the lack of systematically documented scientific baseline data from previous decades. This data gap hinders the ability to assess long-term ecological changes and the effectiveness of conservation measures.

Methodology
To address the absence of historical baseline data, this study employed Local Ecological Knowledge (LEK) gathered from experienced fishers in Punta Allen, the sole human settlement within Bahía de la Ascensión (the largest shallow bay in the Mexican Caribbean).

• Sampling: Semi-structured interviews were conducted with 25 fishers aged 40–82 years (mean age 62.5), representing 90% of the target population with sufficient local fishing experience (mean 39.4 years).
• Temporal Scope: The study focused on reconstructing conditions from 30+ years ago (pre-1995), a period preceding the establishment of the Sian Ka'an Biosphere Reserve in 1986 and the subsequent gillnet ban.
• Data Collection: Using visual identification guides, fishers were asked to identify elasmobranch species present in the bay, specifically those giving birth within the bay. For identified species, fishers provided data on:
  1. Relative abundance of early offspring inside the bay compared to outside areas.
  2. Seasonal residency patterns (duration of stay).
  3. Recurrent use of the bay across years.
  4. Perceived changes in abundance between the historical period and the present.
• Validation: Data were refined in a final workshop with participants to resolve inconsistencies and verify spatial locations using bay maps.

Key Results
The study identified 23 elasmobranch species present in Bahía de la Ascensión 30+ years ago, with 18 species reported to give birth within the bay.

• Nursery Area Identification: Six species met all three established nursery-area criteria (high density of early offspring, site fidelity, and recurrent use) with strong support (>50% of respondents):
  • Sharks: Carcharhinus leucas (Bull shark), C. limbatus (Blacktip shark), Ginglymostoma cirratum (Nurse shark), and Negaprion brevirostris (Lemon shark).
  • Batoids: Hypanus americanus (Southern stingray) and Styracura schmardae (Atlantic chupare).
  • Sphyrna tiburo (Bonnethead) showed medium-to-high support, meeting the criteria with some variability.
• Abundance Trends: Fishers reported divergent trends between the historical period and the present:
  • Increases/Stability: Early offspring of C. limbatus, N. brevirostris, Urobatis jamaicensis, and Styracura schmardae were reported to have increased or remained stable.
  • Declines: Significant declines were reported for Pristis pectinata (Smalltooth sawfish), P. pristis (Largetooth sawfish), Pseudobatos percellens, Sphyrna lewini, and S. tiburo.
• Drivers of Change: The majority of fishers attributed the increases and stability in certain populations to the 1986 establishment of the Sian Ka'an Biosphere Reserve and the concurrent ban on gillnets. Conversely, the decline of sawfishes was noted as occurring prior to the fishing experience of most current interviewees (1960s–1980s), suggesting historical overexploitation.

Key Contributions
This study provides the first application of LEK to reconstruct the existence of elasmobranch nursery areas based on currently accepted scientific criteria (high density, site fidelity, and recurrence). It establishes a historical baseline for Bahía de la Ascensión, revealing that the bay functioned as a communal nursery for multiple shark and ray species three decades ago. The research highlights that while some species have recovered or stabilized following conservation interventions (gillnet bans), others, particularly sawfishes, experienced declines before the study period began, a nuance often missed by short-term scientific monitoring.

Significance and Claims
The paper claims that this is the first study worldwide to use LEK to properly identify past or present elasmobranch nursery areas based on established criteria. The authors argue that LEK is a vital tool for rescuing past information in data-poor contexts, allowing for the evaluation of ecosystem services (specifically recruitment refugia) that coastal areas provide. By reconstructing the "recent past," the study prevents misinterpretations based solely on present-day data and offers a baseline to evaluate ecological changes. The authors conclude that this trans-disciplinary approach should be widely applied to support the conservation and management of elasmobranchs, particularly in regions where historical scientific data is absent.